Guessed by @Ultrashroomz
Living proof that Metroidvanias can be linear and story-driven while still being totally awesome. These are important aspects of the genre, I suppose, but the real essence of Metroid is in that feeling of dread and isolation, the heavy atmosphere it creates. Fusion has these in spades, and in many ways, does more with these ideas than any other game in the series - because this time, you're not afraid of the unknown, but rather, the very much known. Pretty much from the very beginning, you already know there's at least one thing on the ship you can't defeat, and it's trying to find you. This creates an entirely different atmosphere, where you never know just when you're gonna stumble upon the thing and be forced to run for dear life - and every time it happens, it's an unforgettable moment. Beyond just the SA-X, the game does quite a good job of foreshadowing other dangerous creatures throughout the game, adding to that sense of dread, and even the one machine you're talking to is very hard to trust.
You basically spend the whole game diving deeper and deeper into this mess, finding more and more fucked up shit as you go... and when it's time to deal with all of it, the pay-off is huge. The game's third act is so tense, so exciting, and just so memorable, I'm getting chills just thinking back to it. It's really something special. For a franchise that was initially inspired by Alien, this is where that connection was most apparent - and just like Alien is an incredible film, Metroid Fusion is one hell of a game.