Very fun and addicting gameplay loop. Excellent blend of decision making and physics madness. It might not keep me entertained for hours, but I definitely got hooked and didn't want to stop. Got to level 14! Probably could have gone farther to get max non-heat spawning if I'd been more careful, even with the rods all the way down it's too late at that point.
For useful feedback, I would say Music would be an instant easy win. The retro sound effects were well done, but music makes a huge difference, especially if you want to keep people for a little while.
I was happily surprised at how well it performed in web with that many particles running around. No stutters at all. I can only image how nice it could look on desktop after you add a bit more juice to the graphics.
I actually was too engaged to check if there were more control options, but mouse controls are always awkward. WASD is preferred, with spacebar or enter to shoot. Gamepad is even better, but obviously not a priority in a gamejam.