Straight up three stars for this game and let me tell you why.
In the beginning I was definately thinking four or even MAYBE five stars. I love the first 5-6ish levels. Your upgrades actually scale with the new enemies.
But the last 3-4 levels are redonkulous. Every enemy takes like 27 hits to kill, even with nearly full upgrades. So you just die over and over and over.
3 stars