It's not too bad. I haven't gotten any of the really cool powers though. Don't even bother with Dark Vision, it's pointless if you stay hidden.
So far, I only use Blink, and when I got Possession, I thought it was done and I could do some of those cool assassinations, but apparently you can only possess mice. You have to buy the next level. Boo.
So far I wouldn't say its worth $60. Maybe $20 or so.