It's just OK.
I found this game to be annoying... trees blocked my view of the path so I was unable to see how much damage the enemies where taking.
Units had no description of what they did, how much damage they dished out, or how many spaces they could reach forcing you to simply build and find out the hard way.
Treasure is pointless as the slot machine game is pure luck with like a 1 in a 200 chance of winning, spells take too much mana and you don't find enough potions to justify their use, and I've never once found a health potion.
I dislike the fact that I can't sell units, I get no rewards at the end of the stage for having the units, and when I build a unit in the next stage, I don't get to keep my upgrades. Money is almost non-existant and there is no way to earn more in a pinch meaning the entire game can be lost simply because you spent a little too much in a previous level. If I have 3 ninjas that are level 3, then the first 3 ninjas I build in the next stage, should start at level 3. Your main flaw here is that you give us the same amount of money as every other defense game, but unlike other defense games, you remove all of our towers and their respected upgrades at the start of each level. >:(
The fact that defenders couldn't reach the entire path was annoying too... since you have no idea where the enemies are going to spawn you're almost always forced to build enough of everything to cover the entire path. This means you have to build two archers, so why not just let them shoot across the whole path and increase their price to $200? If anything, they should get an increase in range when they level up.
There seems to be no constant strategy to the game either. The first few times I played 8 archers (4 on each side of the path) was enough to win the stage, but ever time after that it took anywhere from 10 to 14 with no clear reason as to why.
I found it annoying that my only potions came from digging but I had to keep clicking the shovel tool to dig. Why can't I just click it once and remain on the shovel until I click something else?
The graphics where nice, the animations where smooth, and the music was good... nothing great but it didn't suck. It fit well with the game. But the gameplay itself was just average.