A few of the levels seem to create an unwinnable situation if you're not fast enough in getting to a certain tower. And by fast enough I mean as soon as the level starts. Waiting even one or two seconds into a level can cause you to be at a major disadvantage or, as I said before, make the level unwinnable..
Really?! Another game with an energy system?! The energy system takes what would be a good game and effectively makes it unplayable. How does it make any sense to limit how much someone can play your game? Please, do away with the energy system.