Halo 2 the pinnacle of online matchmaking: had the best maps, weapons, ranking system, dual wielding, and fun glitches.
Halo Reach such a huge departure from Halo 2+3, it gave us some new ideas that I grew to love: armor abilities, actionsack, invasion, DMR.
Halo 3 It was pretty much Halo 2 version 2.0, there wasn't much difference other than slightly blander maps (although Narrows was legit) and those secondary grenades or w/e their called (flare, shield drainer) felt tacked on.
Halo 4 Better graphics, worse everything. The only saving thing was bringing back Halo 3's Valhalla.
Halo CE Can't say much because I never played it on XBL, LAN parties and online matchmaking are two very different experiences.