It took me a while to figure out I needed to press enter to start, but once I got going it was pretty fun. I liked the player and enemy designs, but the background could use a little work. The colored backgrounds do help differentiate the levels, but I think it would look better with just a single texture like a darker version of the concrete platforms. It was also a little confusing because sometimes when I died I would have to restart the level, but other times I had to restart the entire game. Other than that, it was pretty good! Nice job on this.