I hope you had fun making this game, because few will see more than half its levels.
I wasn't surprised when I saw how many reviews there were talking about the difficulty spike. I mean, level 12 is way harder than the levels before it. After level 12 things started to get really interesting. Introducing the key was a great move. I enjoyed the last level, but the moving orange background made it really difficult at first.
One thing I didn't see ANY reviews about was the sound. Those sound effects weren't great, and there wasn't any music either.
Finally, I wish there was more of a reward for beating it, like a medal.
You did a great job on this game, can't wait to see what you make next.