Metroid Prime 2: Echoes

[OB1]

I get what you're saying but you don't have all of the facts. None of us do. Of course Zero Mission replaces Metroid 1, but if what you and DJ suggest is true and ZM is actually Metroid 0, then that would make Metroid Prime Metroid 1. And again, we do not know exactly when Prime 2 takes place. It looks like Nintendo is reorganizing the timeline, and I wouldn't be surprised if we eventually see a remake of Metroid 2 with the number dropped or changed.

It would actually make a lot more sense to call Majora's Mask OoT 2 since that actually is a Zelda side-story, while Metroid Prime 2 is more of a full sequel.