I've played for about 2 hours, and all I can say is, if you were wow'd when Super Mario 64 came out, this will do the EXACT SAME THING TO YOU. There are no, I repeat, NO pre-rendered graphics in this game at all. The game seems simple, but the game mechanics make most regular platformers look like pre-school PC games. Not only do you have to jump across stuff, but try doing it in a 3D perspective with constantly shifting controls. The music is awesome too, very well done, and reminds me of Dragon Quest VIII's music style. So yay for Nobou-sounding stuff.
Bottom line: If you loved SM64, you should, at the very least, rent this game. You won't be disappointed, unless you suck and fall into black holes every 30 seconds.