That's the whole problem, some of ya'll are expecting MP3 to overcome Halo. It can't. You cannot do a better online system than Microsoft has with Halo. Halo 3 online is going to be huge, there is no way Metroid Prime 3 could overcome that.
Metroid Prime isn't an answer to Halo and never has been. Some people keep expecting it to be, which isn't really fair to the MP series.
Halo 3 is going to be huge. MP3 will be pretty big. There is no way on earth that MP3 would ever outsell, outhype, etc Halo 3. Accept it.