Great, but wish there was more.
The game's quite novel in the way it plays, and it reminds me of Portal to some degree - the use of momentum for puzzles where timing is crucial and you need to do creative problem solving makes for a very riveting experience.
The music is absolutely wonderful. It's so eerie I had to turn it off - it was creeping me out after a while! That said, the sound effects are perhaps a bit loud relative to the music, but no biggie.
Make no mistake: this game is designed to frustrate you out of your wits as you piece together what exactly you're supposed to do after receiving just the basic info. For this reason, I think it would be unfair for me to tell anyone reading the review any more than that *snickers* Figure it out on your own, and leave no stone unturned. You will feel better about it after you *do* figure it out.
Now, why the 9/10? For the level of frustration given to the player, I feel like there isn't enough reward for it in comparison - I specifically remember thinking "that's it?" upon completing it. It seemed to be building up to some important/big resolution and some explanation, but plot-wise seems to leave more questions than answers (leading to the unfinished business feeling). It could use just a little extra story there.
Despite this, I'm dying to play it again! (sorry for the bad pun :P)