I don't remember the specifics of GoO (been a while since i read it) but yeah, I think you're right. Those Sentinels were very cool indeed.
While we're at it, I want to see more variety in the Flood as well. Since we're going to be on a Forerunner structure, it is all but confirmed that the Flood will be in it. The first episode in
Halo Legends showed a lot of cool new Flood concepts. Oh, and then there's this guy, that almost made it into
Halo 2:
http://www.youtube.com/watch?v=76QTdEhLaBk# Would be soo cool to have a Juggernaut.
Also, I would love to see some Engineers as well. They were in the three most recent games (playing a huge role in ODST), and were in some of the books, too. They are actually Forerunner creations, so it would make sense to have them in the game, even if the rest of the Covenant isn't.