Simply holding space was a bit too easy for me. I think it would make a lot of difference if it would be more like a clicker, so you felt you where actually doing something. I didn't see the cost of the upgrades so I didn't feel I made any progress there. Ultimately, not having an idea of where the end was or how far I was from it made me exit the game before I completed it. :(
But even if I had some issues with the mechanics, I liked the concept. And the pixelart is very cute! :D