Beat it on normal mode and gushed about it last night with Andrew a little. Things I particularly enjoy:

-The gunplay. The guns are loud, bullet time is still a huge blast, and the game gives a you varied, organic-feeling levels to play in. Cover-based shooting is done well, as being out of painkillers, and near-death while you have multiple enemies suppressing and rushing in on the dinky little dumpster you're hiding beyond is tense as hell. Also, there's never really a suspension of disbelief in the level design. No repetitive chest-high walls, and lots of cover is degradable.

-Really good enemy AI. You fight several different types of enemies in MP3, including gang members, military, and PMCs, and they all act differently. Street gangs seem untrained, usually standing out in the open, hiding behind weak cover, and jumping/somersaulting around. Better-trained enemies will take cover, suppress, flank, retreat, and all kinds of crap. I beat the game on normal and still got my ass handed to me in quite a few chunks of the game.

-A mature game that is actually mature. The game actually presents things like gang war, poverty, violence, and human trafficking in a believable and respectable manner befitting of a game made by adults, for adults. Enemies are characterized beyond just being "bad guys", and every character has their own believable motivations for what they do.

-The themes. At times, the game seems to embrace total nihilism. He pretty much hates everybody (including himself), as pretty much everyone is shown to be corrupt, violent, or ignorant, and he's constantly talking about how there is no true right or wrong. Over time, as he meets more and more people who risk themselves to do what they believe is right. Then he just starts to realize that there are certain things that any decent person believes in, and even if you can't solve those things, it's better to do anything you can to do something that is at the very least, a decent act.