I actually ended up bored with the game halfway through. I think I quit around the part where you burned down the drug field.
The game was certainly beautiful, and I did like the little aspects they put into the game. The first time fire spread to the surroundings was awesome. The 'high' they gave your character from burning the drug field was also a cute addition.
But I found that I lost interest with the game pretty quickly. There was nothing that really kept my interest.
Hunting had nothing special to it. I think I liked the hunting/trapping aspect for AC3 better. Not necessarily because of the gameplay with the actual hunting, but because there was a more intricate benefit from gathering supplies in AC3 from the crafting/trade side missions.
Assassination/revenge missions were pretty lame from the start. Most were in a wide open field where the only one kill that mattered was the knife to the target in question. Maybe if they had more caves/buildings/rooms where you needed more forethought in your kill it would have been interesting.
The skill tree was rather forgettable. Having to unlock 'normal' abilities didn't lend to anything interesting. They could have probably done away with the skill tree completely. Tie the 'move unlocks' with assassination missions. Have things like health/medicine increase tie in with the craft menu.
It really didn't help that I couldn't get to like the MC at all. He was constantly bitching/whining because of his bad scenario, but right when I was starting to sympathize with him, he would turn into a moronic thrill seeker and say something along the lines of 'grenade launchers are awesome!'
Overall, really well polished game. Beautiful and glitch free. But there was nothing special that drew me into the game to keep me interested. The extra aspects were boring. The MC was unlikable.