I have LEARNED to love TD games if the graphics and gameplay is good. This game lives up to my standard and I see a great potential with a few adjustments.
You warned about the difficulty in advance. And you're right - It IS hard.
And as another wrote, I also think that the difficulty curve is too steep. Some edges needs to be cut and the playability will be increased.
- If you'll make a kind of tutorial or easend up the strength of the hordes in the first part, to give the player an understanding how to combine his forces while setting up defence by using the scarce resources.
That would/ could give a step-by-step understanding of how to build up a strategy in the game.
- A more slow introduction to the different kinds of enemies so you'll get to know your opponents better (and your own forces as well).
As I see it, you'll meet to many different kinds of enemy forces too fast in the game, which for me seems to be too confusing and hard to learn about the attacking forces pros and cons.
It makes it difficult to create a logic defence.
If you'll die to fast again and again the player will lose his/ her interest in the game. With this game I think it would be a shame.