Quake 4 is a decent demonbasher, but if you are waiting for something tactical or marinery, it's going to be a let down. I mean, sure changing to the very thing you are killing is a interesting twist, which could have had lengthy repecussions, but noooo...now you can read Stroggs computer screens and that's it.
It's way better than Doom 3 though, thanks to the macho-militaristic attitude and guns that matter.