Incredible and a little disappointing at the same time.
COD4 has numerous WOW factors. The visuals, the audio, the story and the multiplayer. This game totally justifies why I spent a small fortune on my HDTV and sweet, sweet surround sound. The game is tight and IW did a great job putting all the elements into one terrific package.
The Bad:
COD4 lost points for two things:
1) Lack of online or system link campaign co-op. C'mon, IW, you have to know that people enjoy playing through the campaign with other people. Campaign co-op is an absolute must. It raised Halo 3 just a little bit higher than COD4 because of it.
2) Length of the single player campaign. Way too short. IW sort of shot itself in the foot by making the game so good. When a game is THIS good, you are even more disappointed when it ends so quickly.