Glitchy
The game is good, but runs a bit slow on my computer in later levels. A quality adjustment would be good to add.
Also, if you hit play while switching days it will jump you to the next day. I tried my hardest to work the glitch to see how bad it could get and managed to skip almost 10 days. In sandbox mode I beat it while only defeating about 400 guys.
If it was simply pressing play that did it, the glitch would not be that bad, but when you choose the upgrade screen, it pauses the game, and unpauses when leaving. If you take the opportunity between days to upgrade your stuff you will jump a day, making the game harder for you immediately and decreasing your overall score in the long run. I suggest not making the between days screen paused, just stop the units from advancing, like at the end of the day.
Another thing I wished was there was an Uber Man upgrade for the main turret. With split form and fire arrows added in, I was hoping to three giant flaming Uber Men to be shot every second, but was disappointed. Perhaps for Flash Empires 4?
Overall, not bad, but you lose points for a big, obvious glitch.