Halo 2 runs as a disappointment to Halo Combat Evolved
Halo 2's story line starts where Halo 1's left off, after the first ring's destruction. You follow the story of master chief fighting the covenant aliens, and as the arbiter fighting the flood. The story I must say is just as good as the original's, maybe even better. That's halo's strong point. I can't say much of online play. Sure it nice, but the stages aren't as good as the first.
Halo's campaign mode and multiplay was better in the first one. Sure Halo 2 brags "hijacking vehicles" and "new weapons", "dual wielding" and the "energy sword" *drools. But it doesn't live up. Buy the first one.