The concept is very interesting, but the whole game is very unbalanced.
I would say you made it definitely to hard. Not 'challenging hard', but 'nearly impossible hard'.
I suggest you post this map project in the map development section to receive feedback and balance it.
This could be, highly recommended, different difficulties.
The terrain of the map could be improved, too. You shouldn't fill unused areas simply with trees, but be a bit more creative. If you take a look on other TD maps, like Nightstalker TD, they have a good design around their map, even if it is totally unimportant to the gameplay itself.
Also, your triggers are leaking, take a look on the leak information threads on Hive to fix them. They are also inefficient. You could make them efficient and have 10% of the triggers you have now.
Additionally, you could add a better quest log, it feels very empty at the moment.
Add a valid creator, too, please.