The giant rats are easy, to try get you used to things and powered up a bit... the flowers and flame blob things on level 3 down will hurt you if you haven't picked up anything by then. Looks like I messed up the experience and you gain per hit, rather than per kill.. oh well.
On the plus side, you can abuse the browser's zoom functionality. Click down the three dot things in Chrome and adjust zoom there, or the "burger" menu in Firefox. I was primarily developing it on a laptop with a teeny screen, so even at it's current size, it takes up half the space. That'll likely be the first major thing to fix post-jam.
(Damn, I'm a wordy sod, aren't I?)