Cool!
That reminded me sooo much of the quickdraw minigame on Kirby's Adventure (and on subsequent Kirby games) :P
I definitely agree with 1N5AN3. A plot/story would connect people to the game more, and his suggestion about different guns and about pushing combinations of keys rather than a single key would make it much more challenging (which gives you a great amount of room for creating different difficulties or levels :D). And as deathmental said, a variety of enemies always helps to keep a game very entertaining. Otherwise, the music was appropriate for the sunniness/cuteness of the setting, the gun-twirling was cool, and the slowdown time that occurred when you were expected to press a key was a really neat effect. I'd love to see another demo before the final version is released; I feel like you have a long way to go, but this is an excellent start in my opinion!
Let me know if you need any help coming up with anything; I think this has a massive amount of potential :D