This game is one of the best I've ever played...
Metroid Prime is sort of a recap of the first few games that had come out on the SNES. The whole game is done in first person perspective (unless you are in your ball form) giving the game a great feel.
Enemies are plentiful and come in a great variety of shapes and forms. While playing you'll be forced to be, literally, back to the wall shooting as fast as you can to defeat huge onslaughts of enemies. Bosses are incredibly fun to battle and have just the right amount of difficulty. And, of course, having Ridley in the game makes things almost perfect.
Final word: If you like the old Metroid games and are looking for a good single player game then you need to hit this one up. You'll be entertained for hours and want to play it again and again.