Today I spent a few hours playing Halo2 - after waiting 90 minutes with 1000 of my closest friends outside the Microsoft company store.
The campaign seems to be pretty good, but it has the usual problem with FPS campaigns, where it needs to strike a balance between giving you freedom of action and keeping you to a predefined path. Overall, it's been pretty good, but right now I'm stucking in a room with a floating guy (more would likely be a spoiler). If you know how to get out of that room, please drop me a line.
I'll be on XBox live on and off. My gamertag is CeeEff.