This definitely needs more levels! The current last level is the first, where the puzzle-mechanic is used. the first two levels are like a tutorial to help new players understand the core-mechanic. (Thats good)
I like the graphics style, alhough the rotation of the robot when moving in the diferent directions seems a bit akward. Would be better to use 4 different sprites for that (robot facing north, east, south, west...)
Also some kind of indication, that the door is now open would be nice (change sprite to an opened door, play a sound resembling the opening,...)
Overall: Good job so far! I hope you plan to further expand the game.