Halo CE was good for two things: co-op Legendary, and wacky LAN parties.
Halo 2 was good for two things: wacky LAN parties, and being the Pink Ranger.
The Xbox Live experience for Halo is godawful: the community is comprised of boys too young to be playing Mature games and men too old to be playing Mature games. It doesn't help that Halo 2 was rushed, the single-player was lackluster, and it had more bugs than my windshield.
That being said, yes I'll be picking up Halo 3. I suppose I'll get around to activating my Beta account when it releases, but I doubt I'll play much multiplayer. I am hoping the co-op adventure doesn't suck, and then I will port it to LANs with people that don't scream.