Indeed, the game board changing each level - and different towers being available each time - made the game interesting :) The traps behaving as another kind of tower are also a nice change.
It has quite a few downsides, though. First, as someone mentioned, it doesn't save progress so I can't close it and continue later; I didn't even find a pause button! It's very basic in terms of features: there are no explanations about new turret types or new enemies, no achievements, no difference if you finish a level with all treasure in place or just one last piece somewhere along the map... Also no story inside the game, or even a "you win" screen. I think it does have potential, but it appears as if the changing maps and available towers had better be integrated into an existing tower defense game.