Well, you have guaranteed a main Mario game and at least 3 Mario spinoff each year. And for Zelda we get a new one at least once a year. Metroid is like one per console if we are lucky, so Federation Force was a dagger in the guts for those who wants the original Metroid formula back. (And probably with how badly Other M was received, they went back to the Prime formula).
To be honest, I'm actually looking forward it, a Metroid Prime multiplayer sounds like fun, and as long as it keeps the elements that made Prime successful, I won't mind Samus not being there, or the chibiness of it.