I like it except for the save thing. I can only play in spurts and often I've gotten pretty far and there is no save position to be found. It's a different kind of game with a little bit of everything. I'd check it out by renting it first then buy if you like it.
I only played a little of Metroid Prime before playing Corruption and it didnt really make much difference to me. It was a must buy in my book though because i knew that i liked that style of game.
MP3 is probably best described as being like a first person version of Zelda set in an space/alien setting. There is a lot of shooting but there is also elements of exploration, puzzle solving and a fair bit of back tracking to do (i think these parts puts some people off).
Controls are fantastic (very good on standard and even better on expert setting) and the graphics are very good. The game is single player and should take around 16 to 20 hours to complete. I completed it in 16 but i'll play through it again, soon as i've forgotten it enough.
You could always buy either Metroid Prime for Gamecube or Super Metroid for VC to see if you like the games style first. Even though Super Metroid is a side scroller it has the same kind of gameplay, if you like Metroid Prime then its a really easy choice as MP3 improves on it with much better aiming and targeting.
MP3:C is like a mix between MP1 and MP2:E, except it takes all the best elements from each and combines them into one. it doesnt take TOO long to get something, like in mp2, but it's not like they're throwing gadgets at you like in mp1. you don't have to use beam ammo, but you don't get to change weapons. i don't think it utilized visors nearly enough, as you only get the
near the end of the game. but the bosses were fun and challenging, as were the puzzles, and switching in and out of hypermode was a blast!!