I went in expecting something akin to the aptly-titled "quick draw" minigame from Kirby's Adventure, you know, a "push the button faster than the other guy" sort of game, but I was pleasantly surprised to find a bit of added depth in there. The audiovisual presentation is consistent and appropriate for the theme (with a couple of minor exceptions), and I appreciate the addition of difficulty options, even if there aren't a whole lot of distinguishing features between them. I only have a couple of tiny criticisms with this one.
I'll get this one out of the way first: it threw me off a little that the crosshair didn't rebound off of the side of the screen, since the bullet icon bounces between the edges of the first gauge. That may have been entirely intentional, and I can understand the reasoning behind it, but it came across as a tad inconsistent (I haven't tested it, but I wrote this assuming you can get shot while aiming. If not, it makes sense for the crosshair to drift offscreen).
Somewhat more importantly, I haven't been able to select my difficulty level after dying and resetting the game. As a fan of "Impossible" mode, it's a bit annoying to have to reload the page whenever I want to get my QUICKDRAW fix, but I've learned to live with it.
This one's a bit more of a suggestion than a criticism: I think the game would be more interesting if opponents came in different shapes and sizes. Aiming and firing can be challenging as is, but having to adapt to uniquely-shaped enemies would give it significantly higher replay value in my opinion.
That about covers my thoughts. Great job!