Very polished, very refined game. I chose to build a lot of power towers to 1 click the ghosts to minimise how much I would have to come back, and then just surround the trees with lumbermills and rocks with quarries. In the end, I did enjoy this game, but I think the core gameplay loop could do with some work to make it feel extra special. For instance, some weak walls to surround the crystal would be nice to stop me from losing so much health (although the healing towers can counteract that if you have a lot of them).
Either way, good game!