A gem. Worth playing even years after release.
Metroid Fusion keeps the gameplay of the original games of the series, as Samus roams the game sideways. Fusion begins with Samus's becoming infected by a xenomorphic organism called "X". Subsequent events bring Samus to the space station of a biological research company, where the X have managed to infest all life in the station. The missions follow Samus's attempts to eradicate the X and contain many surprising developments that perhaps not even the most savvy gamer would expect.
Fusion's controls are extremely simple and anyone can learn to play the game very quickly. The game, though it doesn't change at all between plays, is very fun and can be replayed many times; I myself have played through the game at least 15-20 times. Part of this replay value comes from the fun of searching for the multitudes of items to upgrade Samus's health and weapons.
Metroid Fusion has all the aspects required of games of the adventure genre, a respectable and powerful hero (or heroine, as in this case), a nemesis who seems impossible to defeat even up to the end of the game, a large game world to explore, a lot of bosses, and a bunch of surprises. A message to all gamers: BUY THIS GAME!