This is a really nice concept. It's quite fun. It might help to raise the camera a bit, making it a top-down, or either allowing the player and camera to turn. It was a little difficult to see the guards and area around me. For some reason I wasn't able to punch the guards. It may be an animation constraint issue if you're attack conditions don't allow for movement.
And I know time was an issue for all of us, so we had to prioritize certain things (I certainly did with my level design/animations/etc). But if you decide to do anything more with this, it would be cool to have an inside level where the thief actually makes it into the castle.