Metroid Prime 3: Corruption is everything that gamers have been waiting for: a solid, well-developed, long-lasting experience that casts aside Nintendo's "casual-friendly" focus of late for the sake of unadulterated gaming.
The key to the success of this title is quite simple: polish. Every single aspect of Metroid Prime 3: Corruption has been polished to a blinding sheen. The graphical presentation, the control, the sound, the pacing—everything feels superbly tuned. This is a AAA release in every regard, and the work that has gone into the title is evident from the first time you boot it up until the moment you beat it.
This review is a little breathless for my taste. I disagree with them on a few points. I'm only an hour or so in, but the grapple-and-yank move still feels clumsy to me. Seems like the nunchuck doesn't register my yanks very well. Luckily this is rarely used in combat, so I don't have to care.
What did they get right? The controls! Finally! Someone's finally using the Wii controls the way they were meant to be used. It's quite intuitive, and once you get used to it (twenty minutes or so, for me) extremely fluid. I do recommend that you turn the control sensitivity up to either Intermediate or Advanced. And surprisingly, I also recommend "hold Z to lock-on to enemies" as well, it really works. Overall, I've found the controls both responsive and greatly immersion enhancing. I also think the artistic stuff - level design, character design - is quite good. I think the Wii is still a little underpowered as a rendering platform in places, but you probably won't notice.
It's also interesting to see some of the sub-plots in here. In particular, phazon is no longer the slime of pure evil, it's actually becoming useful. (Though that may end up being a plot twist later on in the game...) I also like that for a change you start out fairly powerful. You already have space jump. You already have morph ball and bombs. And the ability to hop while you're balled up by giving the wiimote a toss is great.
Edit: Here's a better review that gives you a more balanced perspective. Their conclusion is that while MP3 isn't flawless, it's awfully darn good. Maybe the best of the Prime series.