Not being able to place new turrets or moving existing ones around during play is kinda annoying, when that one enemy goes beyond your turrets range with a sliver of health and you just have to forfeit or wait the wave out.
It tried it with the catapult, but it is kinda hard to controller where you land and deal damage.
The main mechanic is fun, reminds me of other tower defense games where you as the defender have a more active role.
Overall a fine tower defense game, could use some interesting variations regarding enemies or types of turrets.