I loved Halo 1's single player missions. Yes, including the infamous 'Library.' I played all the missions on all settings repeatedly. Of course, I was about thirteen at the time so my friends and I had plenty of time to waste on games

Now, I hated Halo 2's single player

The first two or three missions were fine, then it got into that whole alien Elite character that I just didn't give a rats ass about.
Both games multiplayer were pretty good though, in my opinion.
I got a chance to play some Halo 3 when a friend of mine brought his Box to the college, but it was only the multiplayer. I haven't gotten a chance to see the single player. But, so far it looks okay...
All in all, I'm just a casual gamer. My friend stood in the line for Halo 3 for about seven hours
I was at home sleeping