Started playing Red Faction Armageddon, and I gotta say, this game has some incredible sound design. Like, seriously, some of the best I've ever heard in a game. One of the most impressive things about it is the ambient sounds, and how they aren't static. As you turn to look around, the sound actually pans to keep it's place in the environment. Most games that have ambient sound just keep it in one channel, so even if you're turning, it stays in the left or right ear. (I'm looking at you, Skyrim!)
Also, the sound of buildings and stuff falling is just awesome, and being able to hear the rubble scrape together as you walk over it is a nice touch. There's also a lot of variety in the sounds, so when you hear a building being crunched, it doesn't sound the same for every one.
Really, really neat.
Oh, also, I just remembered: As your gun gets lower and lower on ammo, it makes a different noise when firing.