Wow, I came into this thinking it would be great, and it amused me for about the first 3 levels. Then the problems started to crop up.
When you win at cards because you've stuffed your hands full of aces that's not tactics or something to overcome it's just cheating. Arbitrarily limiting tower placement to where you (the game creator) decide they should go isn't tactics, it's cheating; that counts both for limiting the number of spaces so a tower can't be place there and limiting towers to a specific type of land. Same goes for locking down the entire map in purity towers and trees so that you can't build anything unless you went for one specific build, and even then you're just less screwed not ok.
Making it to where even if you went for the complete mana + cost reduction you still won't be able to take out a single spawn building because they have too many shields isn't tactics, it's just cheating.
Making some enemies require mana expensive spells in a tower defence, while also requiring other mana spells just to place any towers, and throwing them at you right at the beginning, isn't tactics, it's just cheating.
So all the levels are frontloaded for difficulty. For most maps thanks to the terrible placements you have no choice but to go for one specific loadout and place buildings in a one specific way or you lose (again not tactics, maybe relies on fast clicking and hotkeys didn't work for me, and still cheating). By contrast the endgame was sorely lacking; You have so much mana and enemies rarely make it halfway due to the towers damage.
The skill tree is also lacking. The passive bonus is negligible unless you're in late game (and even then it's just barely there) and you seem to have planned the levels so that the bonuses don't let you get ahead but are, in fact, required to play the level at all. and without them you will lose badly.
I would suggest getting rid of the purity towers or severely lowering their shields, you could make towers placeable in forests and have that severely lower their stats. and instead of land types restricting towers just make it a boost to their stats, or one stat, possibly linked to the skill tree passive ( which you should increase). All this so that you can have each level ramp up the difficulty even further; increase the monsters hit points across the board as the waves increase (give them upgrade bars to show the +HP level same as towers) as well as the ammount of monsters. and instead of complete immunity maybe some of them block a hit or spell every # seconds or every # hit. or armor gives dr that goes away after it breaks (so that the creature isn't just faster)
TLDR; it was amusing for the first few levels, but the blatant, arbitrary, and stupid restrictions on everything make it get old fast. There should always be more than one way to win and this game doesn't allow for that.

One of the greatest flash games of all time, this is the only stable version I've found of it after all these years.

Its good

blam bceause bombs at the end are annoying as hell.
they dont move when they are clicked on some times. and there are too many of them.

Fun

Amazing, is this game made only by one man???