Ok sorry if I sounded harsh (It wasn't intentional but I know I did)
I half expected it to drag into a 'Halo is better than Metroid Prime' debate though (which almost bores me to tears every time they pop up) so I got a bit defensive I guess
The only down sides to Metroid, IMO, are:
The controls do take a long time to adjust to. The L shoulder button is used to 'lock on' to targets - it opens up so many possibilities within the game but it will seem impossible at first for anyone used to console FPS games

It took me about 20 minutes of messing about before I had mastered it though.
Jumping can also be a problem at first but the game very slowly builds you up to the complex jumps - by the time you need to be really accurate with your jumps, you will be. During the beginning, the landing platforms are huge, so you have plenty of room to land. iirc there are no life or death jumps ie if you miss a jump you will not die. You'll obviously lose some health but it won't kill you.
Apart from that I don't think I can fault it. The save points are quite far away but, luckily, they are always in 'safe' areas so if you're running to save and restore energy, you don't have to worry about getting slaughtered in the room before a save point
There's no 5.1 but the Pro Logic 2 sound is excellent - it's as good and immersive as any surround sound I've ever heard in a game anyway. As I said the music is fantastic and it really booms out when necessary, but it is also very tranquil and calm when it wants to be.
It's one of my favourite games of this generation and, IMO, the best single player game ever made purely for the immersion and atmosphere that it creates
And it's not a FPS...it's a First Person
Adventure
lol, that was just one of the ridiculous arguments used during the whole Metroid vs Halo thing
Edit - wow, talk about rambling...mention Metroid to me and I just don't shut up