They won't release it cause they wanna promote Xbox-360s. They want to give you a reason to buy Xbox instead of other consoles.
Well, the game is now released, I bought it yesterday. Cool graphics (way better than Halo 3), nice campaign story/gameplay . The custom game 'firefight' is pretty good too (where you co-op w/ friends to beat unlimited covenants, coming out of doors and spaceships). Its a shame that there isn't a versus-multiplayer mode though.
Anyway, I'll lock this topic. You can always check Grisom's, which is more up to date.