I liked the concept of ghosts repeating your movements, but I reached level 40 and I don't remember there being even close to 40 ghosts. In addition, the ability to quickly kill ghosts meant that they weren't much of a problem. Maybe if the ghosts appeared at specific intervals and were immortal, it would make for a more interesting game.
As for upgrades, I think I would prefer them to improve the stats of specific skills rather than give one-time skills. I felt that choosing the life upgrade twice was better than choosing a one-time skill.
As for the graphics (I don't know if you didn't have enough time or if you're not a graphic designer), you could have tried to make simple rotation animations and use more basic shapes (stars, diamonds, etc.).
To sum up, I liked the idea, but it needed some polishing.