It's a 10 to me. I haven't played a game with so many completely and utterly brilliant nidbits in it before. There are a fair bit of things I don't like about the game, but they're so outshadowed by the brilliant elements. I utterly adored how the timeshift stones were implemented. The boss fights were as a whole some of the greatest I've seen, and the controls were brilliant.
I haven't finished it yet, so I'm not completely certain where it ends on my list of favourite games. It's looking to end somewhere between 2nd and 4th at the moment, though.
Overall, absolutely marvellous game.