If you own a GBA Metroid Fusion is definitely worth checking out.
Metroid Fusion is the most story-driven Metroid game, and for better or for worse, this changes things a bit. The plot revolves around a parasitic species known as the "X" that is infecting nearly every living thing it gets in the vicinity of, including Samus Aran. Absorbing the X will not only heal Samus' health but it will also keep the enemy from regenerating. Fusion plays just as well if not better than previous Metroid games for the Super Nintendo and NES. The game is a great example of the evolving franchise, and the game controls and plays very fluently. Samus can fire missiles, run at lightning speed, evaporate enemies with her plasma beam, squeeze through tight spaces with the morph ball, etc. Metroid fans will be happy to see that the majority of power-ups and abilities are in the game. These power-ups are also creatively used by the developers, adding to the exceptional quality of the game. My favorite aspect of the Metroid series is how as you gain these abilities with Samus, the more you feel invincible and unstoppable, and Fusion does a superb job of presenting this dominating bounty hunter in her finest hour.
While Fusion is a great revisionist take on the Metroid series, the game does have some rather annoying tendencies. A significant annoyance casual and hardcore gamers will find in Fusion is just how much damage Samus takes to the puniest of enemies. Even when Samus is fully equipped with weaponry she still takes a lot of damage to these foes. Some of the boss fights can be a real challenge as well, edging on the verge of frustration in some of the battles. Another problem with Fusion is how the path forward might be the most trivial space in a wall that can be difficult to find; in many rooms you may have to rattle the floor with bombs to find the way through. The urgency to move from place to place also slightly deters from the exploration, as your constantly updated by your computer ADAM. Fusion oddly rewards players with the "best" ending if you complete the game in 6 hours, its kind of a bizarre way of rewarding the player, but I guess it gives you the incentive to play the game again.
Nevertheless, Fusion looks fantastic, sounds even better, and offers a compelling story (who would of thought). It is an impressively atmospheric game as well (not as much as it's Gamecube counterpart obviously) and has rock solid controls. If you own a GBA, this game is definitely worth getting. It's only $4.99 in the USA, and I can't even think of a better experience on the GBA. Fusion is a classic that should be played by not only fans of the Metroid series, but GBA owners as well.