Overall, not a bad game, if a bit basic.
I'm wondering if it's needed to actually press the mouse button to fire. Since there's always something to fire at and no reason to not fire, maybe have the robot buddy automatically attack the closest enemy?
It's nice that upgrades lets you decide on a build (got killed because of -30 health regen, oops), but I'd like it to be possible to choose not to keep skills picked up from chests, especially if they don't mesh well with what I'm going for.
I also found it easy to cheese non-missile enemies by simply standing on the platforms. Making it so enemies can aim vertically would easily fix that.