Playing it for the first time 7 years after release, you'd expect it to feel dated, but it feels like a brand new game.
First let me say that 7 years old or not, the graphics are absolutely stellar, even by today's standards (for the Wii that is). The landscape of Phendrana Drifts in particular is absolutely beautiful. I found myself sitting there for minutes at a time in awe of the snowy environment.
But graphics can't make a great game by themselves, so what makes Metroid Prime a great game? Simply, it takes a hint from modern FPS action, the adventure of Legend of Zelda games, and Metroid's own patented style of action platforming, and flawlessly combines them to form something that can be called nothing but infallible. The intricate screen designs are supposed to be as if you're looking through Samus' visor, and that makes the game all the more immersive. The water running down your visor, steam fogging up your visor, and with the proper lighting, a reflection of Samus' face, they all make you feel like you're really in the Varia suit on Tallon IV.
Don't be put off by the game's age, given the choice between this and Corruption, I'd pick this. Whether or not one is 6 years older than the other is insignificant. It's like comparing Ocarina of Time to Twilight Princess, they are the same basic concept and one has a huge graphical upgrade, but regardless of the order you play them in, OoT will always be the superior game. In fact, speaking of OoT, this is one of the few games that deserve to be mentioned in the same breath as the legendary Ocarina of Time. Trust me, the $50 Trilogy is a gift from Nintendo, the updated Metroid Prime justifies the price tag alone.