Nice :) I played till level 8. There's a couple moments where the design feels a bit troll-ish: the first time the falling blocks appear, you find out as you're jumping across and instantly die on contact, both of them, and they're the same colour as the rest of the blocks, in fact I had no idea what killed me first time, because the block had "started moving" but visually only starts off moving at a crawl, so looked like nothing killed me.
Also I really wish you could shoot while jumping :) the slimes on the roof feel like they were designed for it, made me really want to to do it and I was surprised when I couldn't.
Hmmm, also I couldn't see a way to quit to tell you which level exactly, so I refreshed the browser to restart and use the level select, and all my progress was gone, fine, but then there's a "delete progress" button - which seems to imply it would save progress in the cookies, which hasn't seemed to work?