I don't think there is slowdown...
For my part, it would only be that the character is kinda slow, and there is a certain acceleration to a point, but the controls aren't really good, the gameplay is sloppy. For the graphics, it's really appealing, you got that right, reminded me of Sonic (bees, the waterfalls, the kind of boss). Did it freeze intentionnaly after level one or it's a bug? anyway. you can improve that a lot, the character isn't very appealing, and the "powerups" are random and you can get back to shitty weapon...
And I may add this: What the fuck? The chest hurt me!