If you're new to the Metroid series, this is a great place to start. Otherwise... it's just average.
Now, I'm not saying this is a terrible game. In fact, it's pretty good. It's just lacking.... something. Here's the story: Samus returns to planet SR388, and is attacked by a parasitic virus simply known as "X". The virus fuses her power suit with her body in some places, and other parts have to be surgically removed. She was given a minimal chance of survival, when someone proposed using a Metroid vaccine. Metroids were natural predators of the X, so the virus was erradicated from her body, now making her immune to the X. Somehow, this managed to change her awesome-looking Varia suit, into this ugly Fusion suit. (Hey, just my opinion)
ALright, I'll start off with the graphics. The introduction and other parts of the stroy line are illustrated by hand-drawn images. Those look pretty sweet. The in-game graphics aren't bad either. The game designers paid close attention to every tiny detail in Samus' world, and it shows.
Next up is sound. Honestly, this part of the game almost failed completely. None of the tunes were very catchy at all, and the only familiar one was Ridley's battle theme. Once you've nearly completed the game, it plays the same song over and over again, no matter which area you are in. The sound effects are, for the most part, better. The explosions, cries of the creatures, and mechanical sounds in the background almost make up for the game's lack of good music. I, personally, REALLY hate the sound the Wave Beam makes. But, that's just me.
Now for gameplay. It's the same as all of the other 2D Metroid games. Run around, shoot some creatures, gain new weapons, jump across platforms. Hey, that's all fine and dandy with me... except there is VERY little platforming in this game. Most of the time, you'll find yourself running down another long hallway, blasting more annoying critters. Very rarely will you see a bottomless pit that can only be crossed by hopping across tiny platforms, or something like that. The bosses were kind of a let-down too. Most of them are ridiculously easy. There might be one or two that might give you a hard time, bust for the most part, they're not that challenging. [Like the final boss. :( ] There's plenty of missle expansions, energy tanks, and Power Bomb expansions to be found lying around in random places. There's quite a few weapons, too. I just don't like the fact that once you find a new weapon, you HAVE to use it. (Unlike Super Metroid, where you could equip and un-equip weapons.)
Overall. Metroid Fusion is a decent shooter. It stays true to the Metroid formula, only not as... fun. If you're new to the series, definetley pick this one up. If you're a long time fan.... maybe you should buy Zero Mission instead.