Game has a good start for a nice tower defense, and even though i played it briefly there are couple things which could be developed further.
- The wave system could be rather automatic, that you have some certain time between waves to buy upgrades, that would make the player react with bit more 'urgency'
-The upgrades to the shovel could be described, for example I was rather clueless what the depth of the hole did.
-Maybe add a wave counter? I played for a while but am unsure what wave I was at.
- Adjust the hitboxes a bit, some enemies fell into the hole even though their hair just slightly touched the hole's area.
Apart from those you have a fun game going, and I really liked the variation between enemies rushing your way.