This is actually a pretty interesting study in hype. The game is really above average, and the multiplayer is a whole lot of fun. Multi-player over Live is where the game shines, and that can make up for a whole lot. The ending is really just kind of there, no real feeling of conclusion, just a cutscene telling you that you have now come to the end of the game. You can play through again at higher difficulty, and the levels really are much harder, and the hardest level is really tough.
There are some minor problems with multiplayer over Live, but hopefully they can be fixed by patching. Nothing that is a show stopper, nothing that will cause the game to crash, just a few things that need tweeked.
Now, was I just describing Halo 2, or Perfect Dark Zero?
Both.
This game just happened to receive the rating that it deserves. It's a whole lot of fun, but really nothing that you haven't played before. You just haven't played Joanna Dark in a long time, maybe never.
It's worth a runthrough, and the multiplayer really makes the game a keeper.