Nice game, cool mechanics. I think from a design perspective, it might be better to make the shape appear and increase in size WITHOUT holding the left click. Pressing left click would then activate the shape(even if it's not the full size yet). It's essentially the same control scheme, but I don't need to keep my mouse pressed constantly.

Solid mechanic you got there, with lots of potential. I'm thinking of being able to click and drag to be able to set traps, rotating maybe with keys to make it easier to control, maybe being able to change the scale on one axis independently of the other to launch attacks in confined spaces... Lots of potential here!

Honestly, a simple but solid proof of concept. I think a progression system/deckbuilding mechanic (like the dev talked about in another answer) could easily place this game in the "Flash/In browser Games that you play for hours without realizing" category !

I Liked the music and the idea! hopefully down the line you can add some progression or a scoring system. Great job!