Best Singleplayer Source Mods

[Dune Jumper]

Edit: I made a new list on the Half-Life subreddit. Go there instead.

Steam broke the formatting on this post.

These are all my favorite Source mods. (Or more specificaly, my favorite HL2, EP2, and Portal mods.) If you're looking for really good mods, this is the thread for you! Keep in mind, I've only played a few multiplayer mods, so I decided to make the main list singleplayer-exclusive. Multiplayer mods will be in honerable mentions. The mods are ranked from my most preferred (top of the list) to less preferred (bottom of the list.)
BE WARNED: Steampipe has broken a lot of these mods. Most of them require unofficial patches for them to be playable. If a mod I include is broken and requires an unofficial fix, I will say so. The fixes for these mods can be found at the very bottom of this post. Mods that that currently have no known (working) fixes are not included.

1. Underhell This is easily my favorite Source mod, and even one of my favorite GAMES of all time. The gameplay is amazing and steps away from traditional HL2 gameplay (there is free aim, ironsights, an inventory, hunger, you can bleed out and all sorts of stuff. There are even stealth sections.) The backstory is good (and actually pretty deep.) The atmosphere is great, and the characters are great. There are over 12 hours of gameplay (not including the optional side missions.) Yikes I'm making this too long. You know what? Just check it out yourself. Go. It's worth it.

2. Research and Development REQUIRES AN UNOFFICIAL FIX. I love R&D. The puzzles are clever, it has some subtle humor, and overall has great map design.

3. Nightmare House 2

4. Get a Life

5. 1187 REQUIRES AN UNOFFICIAL FIX.

6. Riot Act

7. The Citizen& The Citizen Returns Though The Citizen has poor map design and overall looks kinda ugly, its still worth a playthrough. The Citizen Returns, however, has great map design.

8. Portal: Prelude Although the voice acting is horrible, it's fun to see how testing in Apeture Science was before GLaDOS was turned on.

9.  Black Mesa (the original mod version) On this list for obvious reasons. Black Mesa is the Source remake of Half-Life we've always wanted.

10.  Transmissions - Element 120

11. Portal: The Flash Version mappack[portalmaps.wecreatestuff.com]

12. Factum Solus REQUIRES AN UNOFFICIAL FIX.

13. Titan: XCIX REQUIRES AN UNOFFICIAL FIX. There is a serious lack of sci-fi space mods for Source. (Titan is the only one besides Dissolution, but in Dissolution you never even see the outside except for a cutscene.) So Titan has visuals and events that you never see in any other mods. At one part you're outside standing on the ship, and you need to avoid meteor showers all Dead Space style.

14. Precursor

15. Flesh

16. CURSE Although short, it is decently fun and there are no other mods like it.

17. Dissolution I mainly like this mod for its narrative. The gameplay in of itself isn't too thrilling.

18. Silent Hill: Alchemilla

19. MINERVA

20. Silent Escape

21. Estranged: Act 1

22. Grey

23. Lambda Wars

24. Midgaard

25. Spherical Nightmares

26. Weekday Warrier

27. Blue Portals

28. Depot REQUIRES AN UNOFFICIAL FIX. There isn't anything super special about this mod. There is only one map. I only liked it because of the great wasteland scenery.

29. Cremation

30. Gamma EnergyREQUIRES AN UNOFFICIAL FIX.[/i]

31. [http://store.steampowered.com/app/290930/]Half-Life 2: Update[/url]

32. The Stanley Parable There is also a better, full standalone remake of this mod available on Steam if you want to buy that instead.

33. Human Error REQUIRES AN UNOFFICIAL FIX.

34. Triage REQUIRES AN UNOFFICIAL FIX.

35. Random Quest Possibly the most bizarre mod I've ever played.

36. SMOD Redux

37. Radiator[radiatoryang.itch.io] REQUIRES AN UNOFFICIAL FIX.

38. Dear Esther - The Original There is also a better, full standalone remake of this mod available on Steam if you want to buy that instead.

39. Attempt to Survive REQUIRES AN UNOFFICIAL FIX.

40. Joutomaa REQUIRES AN UNOFFICIAL FIX.

41. Station 51

42. Aberration REQUIRES AN UNOFFICIAL FIX.[/code]

Honerable Multiplayer Mentions: 
Team Fortress 2 Classic[facepunch.com]

[url]No More Room in Hell[/url]

[url]Zombie Master 2[/url]

[url]Aftermath:Source[/url]

[url]Resistance & Liberation[/url]

[url]Insurgency: Modern Infantry Combat[/url]available on Steam[/url] if you want to buy that instead.

[url]Synergy[/url]

[url]Zombie Panic! Source[/url]

[url]Fortress Forever[/url]

[url]Fistful of Frags[/url][/code]

These mods didn't make the list because they have no known fixes, or their existing fixes don't work properly:
[url]BLACK SNOW[/url] Only known fix works to an extent. However, there are a bunch of texture issues, and even some important models are completely invisible, like stairs.

[url]DangerousWorld[/url] Both the official and unofficial fixes work for the most part. However, the HUD is broken for both of them.

[url]Mission Improbable[/url] Only known fix works for the most part. However, there are a few missing models, which means you'll see some big red ERRORs. There are some other weird bugs, too.

[url]Dino D-Day: The Mod[/url] Only known fix barely works at all. Everything is completely messed up. (You may have noticed that Dino D-Day is a full $10 multiplayer game on Steam. But Dino D-Day: The Mod is what that game is based off of.)

[url]Comatose[/url] Only known fix barely works at all. You can only get to the main menu. The game crashes to desktop if you try to load a map.[/code]

Go here for a list of the best singleplayer Half-Life mods: http://steamcommunity.com/app/70/discussions/0/612823460277370132/


Fixes For the Broken Mods

Keep in mind, these are all fixes/patches. They all require the full mod to be installed first.
--------------------------------------------------------------------------------------
Research and Development fix:
Go to steamapps/sourcemods/Research and Development and open the gameinfo.txt document with any text editor.
Delete all text from the document and replace it with [url]this.
[/url]
-------------------------------------------------------------------------------
1187 fix:
Download and extract the mod to steamapps/sourcemods like normal (make sure to keep a backup of the mod's main folder so that you have two of them.) DO NOT GET THE ROGUE TRAIN DLC. IT WILL BREAK THE SCRIPTS FOR THE MAIN CAMPAIGN.
Download and install the [url]GCFScape
[/url] tool so that you can open VPK files.
[store.steampowered.com]

Go to steamapps/common/Half-Life 2/ep2 and open ep2_pak_dir.vpk.

Extract the materials, models, particles, scripts and sound folders into steamapps/sourcemods/1187. Overwrite all files it asks for.

Take the backup of the mod's main folder you kept, and extract it steamapps/sourcemods again. Overwrite all files it asks for.

[/list]

Be warned: This fix takes up quite a bit of space.
To clarify about the Rogue Train DLC, it works fine and is completely playable by itself. However, it breaks the scripts of the main campaign. Basically, you need to sacrifice one in order to play the other. So if you want to play the DLC, MAKE SURE to keep a backup of the pre-DLC 1187 folder, or else you'll need to reinstall the mod entirely.
-------------------------------------------------------------------------------
Factum Solus fix:

• Download and install Factum Solus: Episode 2 & its hotfix. (EP2 contains EP1.)
  
• Go to steamapps/sourcemods/Factum Solus and open the gameinfo.txt document with any text editor.
  
• Delete all text from the document and replace it with this.[dl.dropboxusercontent.com]

-------------------------------------------------------------------------------
Titan: XCIX fix:

• Go to steamapps/sourcemods/Depot and open the gameinfo.txt document with any text editor.
  
• Delete all text from the document and replace it with this.[www.dropbox.com]

-------------------------------------------------------------------------------
Depot fix:

• Go to steamapps/sourcemods/Depot and open the gameinfo.txt document with any text editor.
  
• Delete all text from the document and replace it with this.[www.dropbox.com]

-------------------------------------------------------------------------------
Gamma Energy fix:

• Go to steamapps/sourcemods/gamma_energy and open the gameinfo.txt document with any text editor.
  
• Delete all text from the document and replace it with this.[pastebin.com]

-------------------------------------------------------------------------------
Human Error fix:

• Download and install the GCFScape[www.nemesis.thewavelength.net] tool so that you can open VPK files.
  
• Go to steamapps/common/Half-Life 2/hl2 and open the hl2_textures_dir file.
  
• Extract the materials folder to steamapps/sourcemods/Human_Error. Merge the folders, but don't overwrite any files.
  
• Go to steamapps/common/Half-Life 2/ep2 and open the ep2_pak_dir file.
  
• Extract the materials and models folders to steamapps/sourcemods/Human_Error. Again, merge the folders, but don't overwrite any files.

Be warned: This fix takes up quite a bit of space.
-------------------------------------------------------------------------------
Triage fix:

Download and install the GCFScape[www.nemesis.thewavelength.net] tool so that you can open VPK files.

Go to steamapps/common/Half-Life 2/episodic and open the ep1_pak_dir file.

Extract the materials and models folders to steamapps/sourcemods/Triage. Merge the folders, but don't overwrite any files.

Go to steamapps/common/Half-Life 2/ep2 and open the ep2_pak_dir file.

Extract the materials and models folders to steamapps/sourcemods/Triage. Again, merge the folders, but don't overwrite any files.

[/list]

Be warned: This fix takes up quite a bit of space.
--------------------------------------------------------------------------------------
Attempt to Survive fix:

• Go to steamapps/sourcemods/attempttosurvive and open the gameinfo.txt document with any text editor.
  
• Delete all text from the document and replace it with this.[www.dropbox.com]

--------------------------------------------------------------------------------------
[/code]

Thanks to Mod DB user s12345 for the Research and Development fix.

Thanks to Mod DB user LordiAnders for the 1187 fix.

Thanks to Mod DB user Paynamia for the Factum Solus fix.

Thanks to Captain Host and his thread for the Titan: XCIX, Depot and Attempt to Survive fixes.

Thanks to Mod DB user RobosergTV for the Triage fix.

[Proud Facebook Mom]

Αναρτήθηκε αρχικά από Dune Jumper:

Αναρτήθηκε αρχικά από Westenra:

Nightmare House 2 crashes to desktop without an error message upon loading the main menu :(

You'll have to download the new version that came out back in November.

This version?

http://www.moddb.com/mods/nightmare-house-2/downloads/nightmare-house-2-2015

I'm pretty sure I did.

[Dune Jumper]

Αναρτήθηκε αρχικά από Westenra:

Αναρτήθηκε αρχικά από Dune Jumper:

You'll have to download the new version that came out back in November.

This version?

http://www.moddb.com/mods/nightmare-house-2/downloads/nightmare-house-2-2015

I'm pretty sure I did.

Did you try this?

///Intro Crash Fix///

YOU MAY CRASH AFTER THE INTRO LOGO, to fix this do the following:

1 - Go to your Steam library, click on games, from the drop menu select tools.

2 - In the tool list find "Source SDK base 2013 singleplayer", right click on it, select properties.

3 - Go to the BETAS tab, you should see a little down arrow under the "Select the beta you would like to opt into" title, click on it and from the dropdown menu choose "upcoming-" and click close.

4 - Steam will download some missing files, when done, restart your steam and launch NH2 again.

[Proud Facebook Mom]

Αναρτήθηκε αρχικά από Dune Jumper:

Αναρτήθηκε αρχικά από Westenra:

This version?

http://www.moddb.com/mods/nightmare-house-2/downloads/nightmare-house-2-2015

I'm pretty sure I did.

Did you try this?

///Intro Crash Fix///

YOU MAY CRASH AFTER THE INTRO LOGO, to fix this do the following:

1 - Go to your Steam library, click on games, from the drop menu select tools.

2 - In the tool list find "Source SDK base 2013 singleplayer", right click on it, select properties.

3 - Go to the BETAS tab, you should see a little down arrow under the "Select the beta you would like to opt into" title, click on it and from the dropdown menu choose "upcoming-" and click close.

4 - Steam will download some missing files, when done, restart your steam and launch NH2 again.

Worked like a charm! Thanks!

Great mod, too bad about the ending.

Can I ask where you found the solution?

[Dune Jumper]

Αναρτήθηκε αρχικά από Westenra:

Αναρτήθηκε αρχικά από Dune Jumper:

Did you try this?

///Intro Crash Fix///

YOU MAY CRASH AFTER THE INTRO LOGO, to fix this do the following:

1 - Go to your Steam library, click on games, from the drop menu select tools.

2 - In the tool list find "Source SDK base 2013 singleplayer", right click on it, select properties.

3 - Go to the BETAS tab, you should see a little down arrow under the "Select the beta you would like to opt into" title, click on it and from the dropdown menu choose "upcoming-" and click close.

4 - Steam will download some missing files, when done, restart your steam and launch NH2 again.

Worked like a charm! Thanks!

Great mod, too bad about the ending.

Can I ask where you found the solution?

No problem. :) It was hidden on the download page you linked.