This game looked like it would be fun, but the decision to make this a click-fest has ruined the fun for me. Some people may enjoy a game where you are frantically jumping around the map, but to me tower defense is about planning defenses, not lighting reflexes.
The single biggest problem is that you can't build while paused and only have a few seconds at the beginning of the mission to build your refineries and set up your defenses before the enemies start coming, ready or not. The enemies don't follow consistent paths and can easily destroy your towers, which means that in the mad rush to get towers down they won't be placed optimally and will probably be destroyed, wasting money that comes all too slowly from refineries.
This snowballs with the fact that your finances carry between missions, so if you spent all your money and barely passed a difficult mission, you'll be broke at the beginning of the next mission. This punishes the player for not playing perfectly and makes some of the later missions basically impossible because you didn't play the early game just right. The difficulty also scales with your finances so you have to be in the sweet spot of enough money to build enough towers but not too much money that your get overwhelmed before you know what is going on.
At least the game isn't as clicky and punishing as it used to be, in earlier versions you had to manually click on refineries to harvest them and turrets to reload them and the tech tree used to be yet another source of punishment to inexperienced players so there might be some hope for this game, but at this point I still don't recommend it unless you like a rather punishing, frantic click-fest.