So good! 5/5 would spend another hour on it! I'm amazed by the amount of polish this game has, the design has that retro vibe with an efficient color palette, the mechanic is straightforward but challenging and super addictive, I can't praise this game enough!
Few tweaks: the music is a bit repetitive but that's okay, I'm hunting diggers, the frenzy mechanic is not explained but I figured it out: it's slow mo when you right click, it'd be cool to have a shorter time between upgrades or have a visual of what triggers them.
Also I can't imagine how you did that mixed physics between ground control and gravity, really quite an amazing game!