You made the first step, and that matters a lot. One change that would make a world of difference would be to make the long range pickaxe auto fire by default. You basically need to use it constantly, and clicking that much gets old really quickly. That could then be balanced by having a temperature mechanic, with upgrades in the store that allow you to fire it for longer periods without overheating, or that make it cooldown faster after firing. I get the feeling you're headed in that direction anyways, based on your planned improvements.
Hi! I didn't notice this comment. I agree with you. I want to primary gun to have a lot of upgrades available for it. It might start in "burst" mode, but when you upgrade to the auto-fire mode the heat gauge comes into play. Great ideas! :D