I'm really impressed by the AI and the faux-realism of Far Cry 2. It took a while for it to really show how good it was, because of the way I play. I'm quick and do my killing from far away, so I don't get to see a lot of the subtleties of their behavior. If you wound a guy but don't kill him he'll crawl to cover if he can, a medic might drag him to safety and try to patch his wounds up. There's all kinds of combat dialog that goes beyond the normal taunts and stuff. When you blow something up with your sniper rifle people will run around trying to figure out who's attacking and from where and the medics will reassure their patients that it's just a flesh wound, etc. As your reputation increases people start to panic when they realize you're attacking, the final guy in a camp will yell false bravado into the jungle if he doesn't know where you are, it's all really good in a subtle way. Stuff you don't notice immediately.
The faux realism is also cool. With some careful stretches of the imagination the wound system makes sense. Maybe wounds before you're critical are just scrapes or near misses. The self surgery you do ranges from the slightly gross (Cauterizing a wound with a wad of matches) to the genuinely hard to watch (Pulling a three-inch nail out from the space between your fingers). The system itself isn't realistic, but it's a step in the right direction. The ballistics are great. Sometimes they're a little wonky, sometimes I've seen bullets fly through solid rock and hit me, but most of the time they're good. Rockets especially. The Carl Gustav has backblast that will set things on fire, and RPG rounds will bounce off of flat surfaces if they hit at an angle.
The fire spreading is really cool, and although all the intricacies aren't really noticed (Fire spreads differently depending on the wind, the moisture, etc.) it makes for some pretty cinematic battles as you set off a chain of explosions that rips through the base, with more going off every few minutes.
Oh, another nice touch. Pressurized explosives, like propane tanks, will skitter around or fly up into the air, the hole in the canister acting like a thruster, before they explode. I've had a few oh shit moments where I shot an acetylene tank in the hopes of causing some chaos only to see it go flying straight at me.
Great game, worth double what I paid at least, almost sad that Space Marine comes out in 4 hours and 41 minutes so I won't be playing it all that much pretty soon.