Fusion wasn't a problem. I enjoyed it more than Metroid I and II, and possibly even Zero Mission, which was like Super Metroid but not as good. Too many Metroid games are samey, with the Prime series being the worst offender; I didn't even finish Prime 3 because it was just too much of the same old thing. I'm glad this game was so different, that made Metroid interesting and fun again.
How are the Prime games the "worst offenders" in being too similar when Zero Mission (as much as I enjoyed it) was Super Metroid v1.10 and Other M (ditto) was Metroid Fusion v1.001? To each their own, but I felt that each of the Prime games at least tried to add their own unique element to the 1st person Metroid experience:
Prime - bring Metroid into 3D better than anyone could have hoped.
Echoes - add in a dual world mechanic, the screw attack/wall jump, increased difficulty, and all-new bosses never used in previous Metroid games.
Corruption - add in all-new upgrades (including ones where you can
finally use your ship), break up the environment into small chunks with easier access, and try to incorporate more NPC interaction and storytelling.
That's not to say that all 3 games were completely successful at what they did (I still find Echoes to be an entirely unpleasant experience), but I don't think you give the games enough credit for how different Retro tried to make them.
As for future Metroid titles, as I have said before I am perfectly happy with Team Ninja being brought back. Just ditch Sakamoto next time, because his atrocious writing and direction is toxic to the future of the franchise.