Needs keyboard shortcuts for the powerups, better money collection, more time to collect when everything's dead, and better pathfinding. That sums up most of the comments so far, I think.
Too bad that your shooting line is so small. I upgraded my front lasers hoping to cover the screen in dakka, but it only made my kill zone slightly thicker.
Miner ships are pretty handy. Pair them with interceptors, they both spawn fast and interceptors can block for your miners. Plus miners can destroy enemies and give you energy for it.
My only complaint is I keep getting locked out from buying new upgrades, even though I have more than enough money to buy others. Is so there's a limit to your upgrades at early levels?
Anyone else get a lucky beast and be unable to get any of the drops since the monsters chose just that moment to start swarming around them? That's every time for me.
And the game will be sooo easy to get all 6 stars :")