Hmm, Metroid Prime games should probably have some time between them alright, but not one per gen. Maybe two...
The thing is though, I think the series is declining again. Unlike many of the sequels to major Gamecube games, MP3 sold less than the Gamecube original. The compilation didn't seem to light the charts on fire either (though I love it). Something has obviously gone wrong with Metroid Prime. I could hazard a guess as to what it is, and I think it's fixable, hopefully they can reach sales of 4 or 5 million on successful consoles like Wii.
A game I'm developing with some friends:
www.xnagg.com/zombieasteroids/publish.htm
It is largely a technical exercise but feedback is appreciated.