Metroid Prime worked because it still looked and felt like a Metroid game, just like Super Mario 64 still looked and felt like a Mario game. It's difficult to tell how Maverick Hunter would have turned out based on the short clips released, but the action seems very different from Mega Man X, it's source material, and it certainly doesn't look anything like Mega Man besides X being blue. Maverick Hunter may have been a good game, just not a good Mega Man game.