I have the PC version here. I fell asleep playing it. I can't find anything fun or innovative except enemy hierarchy and driving the Warthog. I'm guessing it was great for Xbrick, but for PC? If we didn't had System Shock 2, Deus Ex, Thief, Quake 2, Half-Life, Operation Flashpoint, etc, etc, and if it hadn't been bought by M$ and delayed for PC, i'm guessing it might've been good then.
As for the sequel? Pft. I'll play it when its out, then i'll make a better judgement, but i'm hoping they make the gameplay actually interesting.