I kinda agree that the end of a mission tend to be boring. When you pass the tough first waves, no unit can cross the no-mans land created by your first curtain of towers. Might be interesting to have side quest: like gaining some fixed amount of xp for a given tower position. Finish a mission with at least a certain amount of gold. Finish without using spells. Using only a type of tower, and so on.
Anyway 5/5 !
You can add a skip text button. And maybe a speed up button for long animation. Add a mute button. Graphics really great, I like it! I didn't manage to finish the first battle, difficulty is too hard or only people who saw all episodes can finish it? A lot of different attacks, great! Maybe you can add a upgrade system to earn all attacks. But please, PLEASE, modify your awful "Lol, you got killed." screen.