The AI did seem rather dumb- but it was random and not common through out the game.
Stuff where you'd see one baddy showing up on your map, not moving. Go up to him and his face is pressed against a wall or rock, etc. He just stands there, not really moving. One shot, one kill.
I've had some other random stuff happen, like die simply because I got inside of a hummvee and somehow my getting inside it cause it to blow up.
But these things don't happen often, and other wise the AI seems sufficient.