The game IS too hard, but you articulated quite clearly that it was intentional. Maybe adding some text about intentionally high difficulty to the game itself will help a little, since some players may miss the text on game page.
Basic gameplay is obvious, but some more advanced elements elements are not. For example, I did not know you can upgrade towers until I accidentally clicked on one at wave 5. Also, perhaps some way to see statistic of each tower damage / kills would be nice, especially since the game is intended to force hyper-optimal play.
I did beat first level on the very first play, but only with 5 “life” left due to the fact that I did not know that towers can be upgraded.
I did not see any “spells” in game, so I can’t tell anything about them.