I liked it and thought it looked very cool. I especially liked, for reasons I can't quite explain, that the movie was bookended by giant title cards reading "HANNA" in bright red.
But, and I hate to say this, I was surprised by how very very little there was in the way of character motivation. And without that, it's really hard personally for me to care about the "what" if I don't understand the "why."
Overall: I give it a "B." It's got a catchy beat and you can snap necks to it.