I've spent about 18 hours in the game so far. Of that I'd say 4 were spent doing main missions. 1 and a half doing side missions, about 1 hour doing random encounters. The rest of the time has been spent exploring, finding treasure, finding plants, hunting animals, and completing challenges.
The challenges are awesome, much like Challenges in Modern Warfare 2, they're broken into four categories, which have levels to work through.
The Categories are:
Hunting, deals with finding, killing, and skinning certain animals. For example level 1 you have to find 4 coyotes and skin them. Level 3 you had to find 5 wolves, kill them with your knife, and skin them. Level 4 which is what I'm now on you have to get 4 Boar Tusks, and 3 armadillo parts. The hard part is that the chances of getting Boar tusks is about 50/50 I killed about 13 to get the required tusks. The other hard part is that boars charge you, which sends you cartwheeling, and lowers your health considerably.
Survivalist you have to find a certain amount of a certain plant, which isn't that hard if you use a Survivalist map. The only problem so far is I'm not far enough in the story to get into Mexico, so I can't complete my current level.
Sharp Shooter For the first level you have to shoot 5 flying birds, a later challenge has you shooting 5 birds from a moving train, and the one after that you have to shoot 2 hats off two different people, without killing them. The hard part is due to the accuracy of the guns, you'll most likely hit them in the head. The level I'm at now(7) requires me to kill 3 Bears with 1 shot a piece.
Treasure Hunter, you find a map and need to find the treasure, once you find the treasure you get the next map and the next level.
Each has 10 levels, and you get a reward for completing each. Plus a Special outfit for getting 10's in each.
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