Nice take on the theme but unfortunately after I discovered that I wasn't punished when the enemies reach the finish like in a normal tower defense I just let them pass through, speed up 10x and farmed the coins. Also I didn't think your 2nd and 3rd tower work cause I kept lighting the platforms but nothing happen, maybe a visual count of my energy and how much the next upgrade costs would have been helpful. Didn't beat the game a 2nd time since I just assumed you just shifted the camera view to look 2D, hope I didn't miss anything.
edit: almost forgot, amazing audio design, well done