As a single player game, so far it's shaping up to be great. However as a Multiplayer game, its just an average shooter. It doesn't even come close to the deep gameplay and options of the JK series. I am speaking exclusively of the PC game here.
Having never played Halo 2, I can't comment on how it stacks up to that particular game. However...
This game has great graphics and music and a neat, if short SP campaign. The MP, while it can be fun, leaves a lot to be desired in today's market, and even compared to other Star Wars games.