Pretty good; this actually felt like an NES game. A few questions though.
Why can't you attack during a wall cling?
Why A and S as attack and jump as opposed to the more-used Z and X? (Personally I like A and Z)
I'm also torn on the fact that you have to press jump again to wall cling. On one hand it's annoying to have to press another button to do that, on another it's kind of cool for clinging to a specific spot on a wall.
All in all, pretty fun.