Played with the bomber first and got a game over, then learned my lesson and prepared for the wave of small green guys.
Then played with the witch for grinding XP, but my medals for Lv 80 and 100 didn't register for some reason, the rest is fine.
Gamewise I found it easy and like I don't have much say strategically, but I've never played any game of this genre, so I cannot make any comparisons.
All in all, I must praise optimization; this ran on my 10 year old laptop with nearly zero lag (it happened a couple times only). Good job!