Controls are familiar, but can't be customized very much at all. You can tweak the sensitivity of your analog sticks, and that's about it. It would have been nice to have an option to adjust more; the default dead zone is a bit weird. Also, multiple contextual actions are mapped to the same buttons; you can accidentally vault your cover instead of rolling away from it. That's a pain when trying to escape grenades.
The cover mechanic is not as sticky as most games that feature cover systems. It takes some patience to get comfortable with sliding behind an object and staying there, as too much movement toward the edge will see you creeping out into the open. I came to terms with the cover mechanic and now pretty much love it. It will, however, frustrate anyone who doesn't have the patience for it.
As expected, weapon customization is completely overblown! You basically start with a rifle receiver assembly, and add whatever butt stock, magazine, forward grip or shield, barrel, and sights that you have available. Unlocking or purchasing an assault rifle will unlock all of its parts automatically. It's not realistic at all, but believable enough in the universe that it's intended for. Shotguns, sniper rifles, and pistols are handled differently, since there aren't as many to choose from; the options are limited, but still fun to play with. Of course, the "pimp" textures are back, but this time they're joined by more than two dozen camouflage styles and patterns (zebra stripes? yes, please!).
If you're playing for story alone, this game goes by a little too fast - the plot is easily lost on most casual players. It's also a detriment to the game's already short length that the unskippable cutscenes are included in that five-hour play time I mentioned earlier. At least they're well-acted and not too painful to watch. Levels are short and sweet. Good for multiple play-throughs; bad for production value.
When playing co-op, some levels force the players to split up, a la Gears of War. This doesn't seem to be too popular among reviewers in general, as it leaves the players open to getting downed without anyone to revive them. But it also breaks up the monotony, and to be honest the levels are well-designed with a lot of wow factor. Even more attention-grabbing than the levels are the morality decisions, which are guaranteed to screw with your head. If you get the opportunity, I highly recommend trying every choice available to see the results of your actions.
I really only have two complaints about the campaign co-op. First: when playing online with Nick, we experienced about a five-second sync every ten or fifteen minutes. Annoying, but not game-breaking. The other complaint is that the screen can only be split vertically when playing offline.