Halo:CE campaign is one of my all-time favorite campaigns.
I remember 2 being kind of a let down. Didn't really like splitting time as arbiter (in large part because i prefer the human weapons). And of course the ending was a massive letdown. That's not as much of a problem with MCC because you can move right on to the next campaign.
3 was pretty great, especially if you can get 3 others to play co-op.
Didn't enjoy 4 at all. Couldn't finish it.