Oh, and speaking of changing the environment? We did quite a lot of that. While you can't blow down walls or strategic cover points (yet), you can destroy just about everything else in your path, and it'll react realistically to your bullets or grenades. We were especially impressed with the glass, which shatters realistically; bullets will just leave holes with a spider-web pattern, and you'll have to blast it with something hefty (or just a load of bullets) to actually smash it out of your way.
We've only seen two levels so far - Manchester, a wide-open, ruined, urban battlefield with dozens of troops on both sides running around, and the Northern Command Center, set in an actual series of concrete tunnels that the British used as a hidden command center during World War II. Both environments were impressively detailed and well-designed, and both featured Hero Moments - brief sequences where you'll see a fellow soldier about to be torn apart by a Chimera. Kill the Chimera and save your comrade, and he'll fight by your side. You'll often need him, too, as these segments tend to pop up just before you're set upon by overwhelming opposition.
Other details about the game are still a little sketchy. We do know that the game will use the PS3 controller's motion-sensitivity, but Insomniac won't reveal how. There will be drivable vehicles as well, but the developer's keeping mum on what kind. We also know that the story will unfold from a third-person perspective (meaning it's narrated by another character, while yours remains mysterious), and that the US also factors into the storyline as an isolationist regime that, for whatever reason, hasn't been overrun by Chimera. Finally, we know that Resistance: Fall of Man will "definitely, for sure" be a launch game for the PS3, so early adopters looking for a dark, versatile shooter should keep an eye out for it.