doing that was the biggest mistake of the franchise, IMO
Other M bothers me much less because that was contained in a spin-off with a unique tone... it was fun, and uh the zero suit was looking better than ever thanks to Team Ninja, so right from the start we set a different expectation for what that game was about.
In other words: I don't mind exploring other tones and styles for the series, but they should be kept in separate spinoff games. Let's have Metroid Pinball and Other M and all the rest, but keep Prime ultra focused on the isolation that was always its calling card.