The main mechanic of picking up the key really gave me Mario 2 vibes. I really liked the challenge of level 3 and wish the were more levels. I played on a Xbox 360 gamepad, and didn't run into any issues or bugs in my playthrough, so good job implementing that option! Would have liked at least some sound effects in lieu of no music, but unfortunately there were no sounds at all :((
Otherwise, with the movement feeling solid, the core mechanic being simple and effective, I thought this was a nice effort. I would play again if more levels were added!
Well done!