I'll admit that I was a bit nervous about making the classic yet another FPS, but they did a HELL of a good job with the game.
The music is new, but if you listen carefully, you can hear the original tunes in most of the songs (and those that don't, they sound just like how metroid songs should sound).
They have all the stuff from the original (except jump-n-slash, which was too powerful, and they still -could- have it and I just haven't found it yet), plus a whole new assortment of stuff for samus' suit. You even start with the stuff you have from the original, except the ice-beam, but you get a grappling hook and powerup beam to make up for it (and you are forced to lose everything before you land on the planet).
You have different armors and visors, so it adds to the whole "I'm in a powersuit" feeling, plus the visors add to the element of the universe, and make you feel more like a 'bounty hunter' than a super being out to just shoot everything up.
Lastly, the plot is just great. Its kinda thin at the beginning, you get little pieces of it, then a big chunk smacks you in the face. You think you are close to the end, and find out your not even close (well, I haven't finished it, but I thought I was close, and know that I'm quite a ways off, so I guess that statement isn't backed with proof, yet). The world is ENOURMOUS (and you have to go from end to end to end, until you start finding new areas, and so on).
All in all, I think with metroid and zelda, Nintendo found a way to combat PS2's backward compatability and XBox's online service. If Zelda is half what metroid is, might I suggest you add "Gamecube" to your "should I get an Xbox or PS2?" question.