The game starts off looking and playing quite a bit like Doom3 (which I hated) but it gets better later on.
The missions played from inside vehicles and the boss fights are definitely the highlights of this game. However, most of the game is just running and shooting to destroy another Strogg target (and whatever gets in the way).
The system requirements to play this game at high graphics quality are quite steep. My PC could play Half Life 2 at 1024x768 with AA and AF but I'm forced to play Quake 4 at 800x600 with medium quality to get a decent framerate.