My experiance is quite similar to the comment of Dragon's Isle Software. Once I found a stategy that worked (roots in 4 corner, then tower to protecte each, later expand north and south as it doesn't attract foe) it became easy to repeat the same strat for other levels. I think randomising the spawn direction of the enemies could push players to try new strategies. When a arrived to the tile cornor lvls, I stared to have performance issue (too many enemies) so I did not managed to test further.
For UI/UX, I had some trouble reading the font. Sometime the droid became unselected and it took some time to realise why I could not move.
I hope this feedback will be usefull. Good luck for the rest of the developement !