Very polished entry, I really enjoyed it! The audio and visuals were really well done, and the gameplay felt very satisfying - I managed to beat wave 5 :)
A couple of comments I had:
- Resetting the ghost position every wave felt a bit annoying, I think the ghost should just stay in the same position.
- This might affect the balance too much but... I thought it would be cool if the ghost could pass through solid objects but the zombies and skeletons could not :) That would add another layer of strategy.
Overall, really good job!