Generally I like the concept its really fun to run away from the enemies with my towers. Its refreshing since Ive never done something like that! But I think there should be a possibility to kill the enemies. Not with towers! Maybe some enviroments kill them, so I have to bait them into those.
The camera could help me more. Its pretty hard I think, but the camera is never where I need it (because Im occupied with building). It would be better if the camera follows me. Meanwhile I can give it a offset with the WASD movement that you have (which works, but can be expanded upon). Also the camera could be between the enemies and me, so that the camera tells me who Im running away from.
Well done on that entry, cheers :)