I DON'T KNOW WHAT GAME I SHOULD BUY

[Runcar snowpen]

Hey, I've got 20€ right now and I don't know what game or DLC to buy, I'm gonna start playing Borderlands again and I like Open World / Sandbox / Action / Adventure etc games, what are your musthave DLCS and Games?

[Hurt Me Plenty]

Two sandbox games that come to mind for me would be Garry's Mod or Terraria, both of which go for $9.99 USD (though there's a high chance you already have one or both of those). As for action games, Duke Nukem 3D, Serious Sam HD: TSE and Serious Sam 3: BFE are all first-person shooters that provide a fairly wide range of action (especially TSE) with the first two games being available for $10-15 USD (Serious Sam 3 normally sells for $40, though there are 90% OFF coupons that traders will often give away for a card or two).

[RegionalDialect]

It's hard to suggest DLC for you when your profile is set to private so we can't see your games.
But anyway, musthave games?
-BioShock + BioShock Infinite (as well as the Burial at Sea DLCs)
-Batman Arkham series
-Mass Effect series
-Tomb Raider 2013
-Civilization V

[grounded in reality]

TF2 premium.

[Jazz59107]

Fallout 3 GOTY
Fallout: New Vegas GOTY
Gunpoint
Monaco: What's Yours Is Mine
Mark Of The Ninja
Guacamelee! Gold Edition

[Ineffable Anathema]

Don't Starve
Torchlight 2
Batman series
Elder Scrolls series
Arx Fatalis
VTM: Bloodlines
Serious Sam series
DOOM series
Painkiller series
Hard Reset
Wizardry series

[Shaggy]

CSGO
CSS
Dont Starve
Tf2

[Fork_Q2]

Anything I own.

[TheAnonymousGoat]

Everything he owns

[MEOWMEOWMAN]

Evrything I own = Humans -> Everything what humans own

[Littlefoot]

Either this game:
http://store.steampowered.com/app/203160
or this game:
http://store.steampowered.com/app/202170/
They're both great games near your 20€ requirement.

[Morti]

I have been having alot of fun with a game called "Broforce" lately, it's really good!

[Runcar snowpen]

Okay, thanks guys!

[chibilibi]

The Orange Box. It's 5 incredible games for $20. Don't know how much that is in Euros, though.

[Fork_Q2]

Originally posted by FuG chibilibi:

The Orange Box. It's 5 incredible games for $20. Don't know how much that is in Euros, though.

€18.99.

[The Damned]

There are lots of smaller games that could use up that budget, and give you lots of options. I know it's not exactly sandbox-ish, but FTL: Faster Than Light is cheap and fun, and there are lots of things to uncover in it.