Catchy music, spectacular sound effects, simple controls, and classic designs for the character and background.
The "break the game" option certainly was different.
The barrier for what's tangible and what's not isn't clear, especially for the end where I sometimes mistake it for a trap and vice versa. For example, level 44 I couldn't tell where I could enter and where I couldn't. You should darken the lines for the places people can't enter. The invisible boxes were also a pain and the game was rather short.
Overall, the game was great, but seemed a bit too short. You have the fundamentals in this with the music, controls, and sound effects, but nothing really stood out. The levels seemed too short as I was done with the game within 5 minutes despite all the levels. Perhaps change some levels a bit, add new enemies and obstacles? I know this is suppose to be a simple game and the first game you made, so I understand that it's difficult to factor in extra elements.