RNG plus Tower Defense with extremely limited placement slots is not a good combination, doesn't matter who you ask.
I like the idea of it, but getting through the opening is a pain. Your tutorial gives us a look a magic but we have to complete the third stage to actually get magic that could have very well gotten that ONE last guy who slips through, and some of the units just don't seem worth the investment like the Giant Naga's higher cost for slower attacking speed and the extra mana gain just doesn't feel worth it compared to the Deertaur's better abilities for the same price or the all around faster Fairy.
Honestly this game has a number of issues, but for me, all of the above results in a problem that I see with a lot of fetish games. The early game is a bit too quick to ramp up difficulty.