This is gonna be a long review. Mostly because I am going to add some tips in it.
I have now played this game for almost 8 years?

Anyway the game is completely free to play however can be a bit grindy at the start.
The game used to be pretty P2W, but that old system is gone. So if any review you are reading has the word "Membership" in it then don't worry, that is no longer a thing in the game.

I recommend trying the game and if you have already tried COTW keep in mind, classic has some differences in it.

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When it comes to differences between COTW and Classic the few large ones are.
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§ In classic you HAVE to use the correct ammunition for the animal you are shooting.
Unlike cotw where you can delete a ptarmigan with a .470 nitro express and still get paid for the blood splatter and fur bits that it left.

In classic that is not a thing and if you get an unpermitted kill that animal wont give any gm$ nor will it count as a harvest. Only thing you get is an angry letter from Doc.

You can check the permissions for ammunitions in the store, thehunter classic official wikia or guides.

§ Classic has no "Feed Zones" where animals will always be at (Unless you are using some sort of bait barrel or such) Then I suppose you could count that as a sort of feed zone.

§ As far as I know all animals will already be spawned in the map when you start the game, so you wont just see a deer spawn right infront of ya face. (Correct me on this if I am wrong tho)
Due to this you won't see overgrouping animals that aren't supposed to overgroup. So animals tend to be spread far apart from eachother.

§ The animals in classic act quite different from cotw. Some spook easier and they will run a lot further than they would in cotw.

§ Animals can hurt you in Classic, but not by running into you. Rather in classic you only get injured if the animal is directly attacking you.

§ Temperature matter in classic.

In Bushrangers Run and Piccabeen Bay you need to wear thin clothes and/or bring a water bottle. If not the sun gods will smite you with hyperthermia thus killing you.

In Whiterime Ridge you need to wear a winter suit and if you want a tent it has to be heated. If not you will be sent to helheim thus dieing of hypothermia.
I also recommend wearing shaded sunglasses, unless you are like me and enjoy feeling like you are constantly getting flashbanged.

§ You can't jump in classic. I know it's tragic.

§ Lastly. You are able to get everything in the game for free by grinding (Unless it is literally unavailable) Content is released extremely slow, but it is an old game so the fact it's getting updates at all is pretty great imo.
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Tips n General info

If ya found this review and you are wanting to try the game. Then here are some tips n info I can give that hopefully helps.

Info
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§ Gm$ is an inngame currency you acquire from doing missions or harvesting animals.
For some animals such as deer you won't get gm$ if it is a female. Due to the trophy part of sed animal being the antlers, so female reindeer give gm$.

§ Em$ is an inngame currency you acquire from either purchasing with real money, competitions or seasonal events (Halloween, Christmas, etc)

§ The CSS score for an animal is the amount of Gm$ you get from it.
(Example): 40.7 CSS = 41 Gm$)

§ Trophy score as far as I know, does not really have any impact on the harvest. (Again correct me if I am wrong)

§ Assuming you have done the toturial you probably already know the controls. However here are some ya may not know about.

"X" Lets you move ya head around.

Hold "T" to do different emotes.

Hold "G" to check how effective ya camo is or play a game on the huntermate.

Press "H" to hold nothing.

Press "F3" to pull up a session window (Only works in multiplayer)
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Tips

§ Like I said further up. You have to use the correct ammunition for the animal you are shooting. Unpermitted kill means it's now worthless.

You start with a 243 and 12ga single shot shotgun. The 243 can shoot medium sized deer and smaller animals such as canines and felines.
The 12ga however can kill larger animals however from a shorter distance. Birdshot for small game, buckshot for canines, felines and medium game. Lastly slug for medium to large game.

§ Don't aim for the head, instead aim around the shoulder of the animal. Around behind the upper front leg, as this is where the lung and heart are.

§ Tracking in the game can be frustrating, sometimes the game might tell you to go one direction, but the track is going another. If you track an animal and the track is going further than the "V" on the huntermate with no sign of another track.

Go back and try to go along the edge of the "V" or even go fully right or left away from the "V"
as the animal might have gone a complete different direction than what the track is actually saying. Some animals although have larger spaces between tracks (Such as reindeer)

§ I highly recommend doing missions as they give a large amount of gm$ and if there are some missions you are having trouble with or can't do. The community of this game are extremely helpful and often quite willing to help others with missions or such.

Daily missions are also a good way of getting gm$ however you will have to keep a daily streak to get a good amount of gm$ out of it. However some can be a bit difficult, so if you don't have much freetime then it might not be the best option atleast streak wise.

§ For what animal to hunt to get the most gm$ in the quickest way.

Geese are probably the best option, however you need a goose setup for that.
Turkeys are also good, but quite slow and you might want a setup for that too.

Coyotes and Red fox can give a good amount of gm$ and usually come in fast if you have a jackrabbit caller.

European rabbits can also give an alright amount of gm$, however can be slow to hunt.

To hunt them you can find a nice rock to sit on around 15-25m away from their burrows and then simply aim in the direction of the burrows and wait. You will hear digging sounds and a rabbit will pop up and then fire at it.
Kinda like a game of whack-a-mole, but with a shotgun.
Bushrangers run at copper hills can be alr if you wanna go for euros and fox.

§ Lastly. If you don't know what gun to get as the first gun you buy (With either gm$ or em$) Id usually say it depends on what you are going to mostly be hunting.

Here are atleast my personal suggestions.

Small Game
12 ga pump (6 shells, able to use scope)
10 ga (Strongest shotgun in the game, 6 shells, unable to use scope)
17hmr (Not good as the first gun to get, but I still recommend getting it at some point)

Medium Game
300 Boltaction (Powerful and reliable, usually the go to starter rifle)
7mm Bullpup (Quick firing rifle with a mag of 5 bullets)
9.3x74R O/U (Powerful twin barrel rifle, sortof quick firing, has abit of bullet drop)

Large Game
340 weatherby (Very powerful rifle able to hold 3 bullets)
45/70 leveraction (Powerful and fast firing rifle, able to hold 5 bullets)

Both advanced guns are quite good IMO, the drill gun being prolly the better option.
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If you have any questions please do comment. I also would be down to help with either getting started or with missions if you need. (Unless I am busy ofc)