I have to agree with you on the ODST's campaign; I still liked it, but after seeing a couple trailers (especially the one with I was getting pumped up for some insane large-scale interplanetary paratrooper fighting from the perspective of 'one of the guys,' but instead we got an action-mystery game. But hey, it was an action-mystery with Nathan Fillion
Also, I dunno if I would've done ODST before Halo 3, but I guess it doesn't really matter either way. They both only really cross paths for a little bit, and then both stories go way off in different directions.