Well, I bought this game earlier today. I've been really excited for it based on some developer interviews in the past and being a huge Potter fan. If you're getting this game for the OOTP story, pfffft. If you know the story well enough it'll be alright, but I figure anyone that doesn't know the HP story is going to be awfully lost. Otherwise, the game is pretty enjoyable.
Cut scenes are very awkward as they jump around a lot. The wand control is pretty fine so far. Sometimes it's a little hard to target something properly, but I've only got about 45 minutes of game play in. I've already founds lots of little "environmental magic" throughout what little of the castle I've seen. By this I mean broken suits of armor that require Repairo, or cupboards that can be opened up for discovery points and such.
At any point it seems you can just run off on your own and do whatever. I've already been pulled into two minigames (Wizard Chess and Exploding Snaps) and one duel. So all in all, I'm pretty pleased with the game. Thumbs up from me!