Its an epic game, I couldn't put it down and I had it beat in 6 hours. I loved the story line, and I think that if they made a movie from it, it would sell well.
I wouldn't compare it to Halo 3 though, since the experience on the console is so much different from the PC (Unless your comparing the console version of CoD4).
My favorite part of the game is when
click to show spoiler
the nuke just went off and the helicopter crashes and you crawl out the back of it and die