I was surprised reading reviews about Fusion (outside of backloggd), because of how polarizing the views on it are, but I can understand it. It's not the most fun Metroid, the bosses are kind of hit or miss, and it requires patience by the slow pacing. But it does everything else so well, that I personally couldn't care less. It's so effective at creating an oppressive atmosphere, that as a 2d game it's pretty impressive. From the context of the mission of you stranded on a spaceship, to the infestation, you being separated from your suit, to being distrustful of the voice guiding you, a copy of yourself that is hunting you down... This might as well be a horror game, lol. And by being more story oriented, it created an emotional impact similar to Super's that I was not expecting at all. I might be wrong, but I can't honestly remember a single old 2d game that was able to make me cry like this one. That alone puts Fusion on top so far.

Overall, I think Fusion is a lot more mature than previous entries, and it should work as a reminder that not everything about a game is its gameplay. Don't expect something similar to previous Metroids, and you'll probably enjoy this.