Fusion despite being linear, had you looking for things by yourself most of the time, Other M was purely linear.
Fusion improved the gameplay from Super Metroid, it felt smoother, slicker, and got rid of most of the flaws from Super Metroid's controls, Other M felt like 2 steps backwards from Prime control-wise.
Fusion introduced new gear, ranging from the Fusion Suit to the Ice and Diffusion missiles, maybe it's my faulty memory but I can't remember any new upgrades from Other M.
The only boss who returned from Super Metroid in Fusion was Ridley, who's a staple of the series and appears in most of the Metroid games, Again, maybe it's my faulty memory because I haven't played Other M in a while, but I can't remember lots, if any original bosses in Other M.
I'd list some other stuff but then again why am I arguing about Other M in the middle of my Uncle's wedding.
