Metroid Fusion takes the vast exploration of Super and splits it into smaller chunks - levels are largely sectioned off from each other and while each is kind of a mini metroidvania map in itself, the game is very much a linear progression that holds your hand on where to go. Combined with a revamped control feel and heavier emphasis on combat Fusion can sometimes feel more like an action game with some exploration than a "true" metroidvania
Now, that sounds pretty bad right. But here's the thing: on its own merits Fusion is REALLY fucking good. That previously mentioned revamped control feel? To accompany the newly placed emphasis on action Samus is no longer a floaty tank but an agile glass cannon with the dev team's work on Wario Land 4 helping inform how snappy Fusion feels. The emphasis on action means lots of boss fights and generally they're very dynamic and exciting, with figuring out how to beat them being half the battle and actually executing your strategy being a decent challenge. Fusion also looks fantastic, especially when using color correction to match how it would look on the original non-backlit LCD. The sound is slightly disappointingly just average overall, the GBA's limitations hurt some of the tracks and some of the sound effects aren't as satisfying as they are in Super.
Good game