Dont judge a book by its cover
At first I thought, one screen?! And then, wow, was I impressed. Just the fact that you made such an engaging game in one screen is success enough, but the game mechanics, 8-bit graphics and diversity - platforming, puzzles and boss fights - were also well done. I enjoyed the leveling up aspect as well. And to top it all off, you threw in some replay value with 3 endings. Goes to show games don't have to be complex to be awesome. My only criticism's were the translation was a little off (not your first language, so can't really dock you there), and the hit detection was somewhat of an issue when getting hit. Well done sir!