Did the Halo series went downhill after CE, could Reach bring it back up?

[slowmo]

Halo 2 was a disappointment, Halo 3 and ODST were fun and enough epic moments to pull it back on par with the first. This is of course purely from a campaign standpoint. I guess 4 player Legendary coop campaign this generation was a much more enjoyable experience for me hence the high regard for 3 and ODST.