The finale was great. I've been reading on the 'swim boards that some are thinking that this is the series finale. And if it is, it is sort of a fitting end to the show. But given the little wink-and-nod at the at end of the credits, I'm willing to bet that Season 5 is just going to be a long time a coming, but it'll get here.
Overall: I loved the resolution of the OSI and Col. Gather's arc. The prom was the "B story" to all the characters, which was good. The Monarch and Dr. Mrs. The Monarch really come off as assholes; which is fine. 21, I think, had a natural and completely deserved collusion to this part of his character's life.