Still a bit easy and room for improvement
Exceptional visuals, I can easily say no other defense game goes quite to this length or style.
However, the gameplay was a little under par. I was able to get through every single level with archers and ninjas with minimal effort. Once I was able to afford dragons, it was essentially game over, as all I had to do was put 2 dragons on the field and wait for them to kill off everything that came anywhere near them.
Another itching factor was the Slots minigame.. why make a game that would help so much in bridging levels be complete luck? Even if it was a small amount during the early levels it would help. I eventually found myself AVOIDING picking up treasure chests just to skip the damned thing.
Some suggestions might be to revamp the characters' stats a bit to make useless characters worth buying, Providing a shop where players can buy potions or even upgrades for maxed out units, being able to save unit experience, some kind of plot, some cutscenes to add some story to it (any level of story is better than none) because a "Congratulations! You stopped the bad guys 'cause you rock!" doesn't feel quite as rewarding as an ending cutscene where your character and whatever lead figure speaking about the situation and such, also making the end levels more climactic... as I said already 2 dragons killed everything in sight and my 12 mana pots I had stored up finished off anything that somehow made it past (A solution to this might be "Hero" or Boss monsters that have special abilities like moving faster or disabling a units' ability to attack)
Well, that's all I can say about it, hopefully it helps.