Neat concept, but the lack of any kind of decision making turned me off a little. The towers don't interact with you at all, which means that you just press E and don't really care about what tower got placed where. All of the towers costing the same as well leads to the very simple gameplay loop of get 5 coins > press E > shoot the enemy closest to the finish.
Something to spice up the gameplay and introduce an element of decision making to the player would go a long way, some suggestions:
* Placing a tower at 10, 15 and 20 coin intervals would place down a stronger tower, letting you decide on many weak towers, or fewer strong towers.
* Towers interact with the player in some way - a tower could give the player a speed boost in its area, give the player more damage when he's around it, generate pick ups or coins that expire over time, making the player want to be near them. Basically anything that would make the player care about what he placed down - not just "more damage that I have 0 influence over anyway"
The intro is neatly done, though, and the graphics aren't too shabby either! Well done :)