Not only is it one of the greatest games ever made, but it's one of the only games ever made that never gets old...
Gameplay : The Gameplay sucks you in....it's hard to describe the exact appeal, i guess if you've played any other 2D Metroid games, then I only have to say it's the best example of the formula, and if you haven't, then you're missing out. Just jumping and shooting through the many areas is awesome, the control scheme and the way Samus handles makes this game just plain fun to explore and enjoy.
Graphics : Fantastic! As good as any 2D game ever seen on the Playstation, and, more than just a few good sprites, a simply great art style and look permeate the entire game, not to mention the gigantic bosses and beautiful environments.
Sound : Always fitting, often haunting, and constantly filling the game with an original mood and ambience that few 16-bit games were able to achieve.
Replay Value : I can't think of a single game I've played through more times...besides the 3 different ending's (None of which are all THAT different from each other :) ), the personal challenge of trying to get the lowest time and the most items possible, and just the sheer enjoyment of the gameplay, keeps you coming back for more....my personal best? 2:25 and 92% of Items...anyway, get this game at any cost, like any other good SNES game these days, it's hard to find, so snatch it if you see it!