Metroid Fusion is not a metroidvania, but goddammit is it not a top 2 Metroid game. There's been plenty of analysis done on how Fusion's atmosphere is so creepy, so to spare you, I will simply say that I agree. Fusion is in fact my favorite Metroid game, and when someone asks why it's honestly a bit hard to explain... it just kind of is. Something about Fusion works so well. It was for so long the end of the Metroid timeline, encapsulating such an iconic franchise in mystery for nearly two decades. It is one of the few 1st party Nintendo games that has genuine horror elements, ones that are executed essentially perfectly. No you cannot infinite walljump, but the gameplay feels great. Fusion has excellent sound design in general, but as a GBA game it is unbelievable at times. I think the reason that I love this game so much is that games like Super Metroid may encapsulate the 'metroidvania' part of the Metroid series, but Fusion perfectly encapsulates the sci-fi horror part of the franchise that I have come to love so much. For 18 years, Fusion carried the most recent weight of what it meant to be a good, new 2D Metroid game, and has always been as an important a part of the legacy of the franchise as games like Prime or Super are.