this game needs some kind of uber-hard survival mode. as it is, it's too easy
most of the guns and backpack upgrades are available from the beginning, and can be had with very little grinding. I think the game is a little 'too open' in that regard
there's too much info on the map/mini-map. there's a lot of cool stuff to look for, but if you're even near it, it shows you where it is on your mini-map. even worse, there's complete loot and item maps you can buy, and again they're available from the beginning if you have the money (that's really something I would expect to be held out until later in the game)
one challenging thing is the AI. it's very good at swarming you, flanking, and investigating sound
edit: the map also shows the areas specific animals are in. that plus the ease of fast travelling takes a lot of the challenge away from crafting