A game that never evolves past the first level.
Ignoring the Sonic/Mario references, this game lacks something that would otherwise make it a great game. As it stands, it's an average game. That is, it's not BAD.
Despite different enemies and backdrops, nothing seems to change in the game. I'm thoroughly disappointed it's the same boss every stage, with a minor power-up each time.
If I could suggest anything, it'd be a change of game play. Make some levels multi-story, add some elevators, allow the player to actually fly (which DD seems to be capable of).
Incidentally, for some reason, 2 tutorial screens whizzed by at the start, so I had to mash the keyboard to figure out the controls.
The sprite looks nice and I like that it has a waiting animation.