I would say it's based on luck to an unnecessary extent, which makes it frustrating, especially considering the time between runs, including the first hardcoded bit of the tower.
There are exponentially many possible situations so you can't learn to deal with them all, and some situations require you to be too far down the screen to react soon enough. It's inevitable with the completely random enemy placement used.
It is still pretty skill based however, although a lot of it is the player's skill within this one game, which is somewhat discouraging as that skill is wasted.
Music is nice, graphics are nice but I think the colour choices and the character's sprite could be better perhaps.