I picked it up yesterday and played for a couple hours. (I just landed on Bryyo) I'm still trying to get used to the controls though, it feels weird. It probably doesn't help that I have a small TV - Advanced aiming is far too sensitive for me to use, so I'm using Standard. I think I'll get used to it though, at least I hope so. If this game can't convince me of the Wii's potential, I don't think anything will.
Still, one thing that keeps me from enjoying the game is being the complentionist I am, I don't want to miss scans, so I constantly have the scan visor on. (this has nothing to do with Wii of course) I'll probably post more impressions as I play. Right now though the game feels very un-metroid-ish because of all the other characters in the game. I haven't been isolated yet, which is what Metroid is about.