Quite a neat little experience! Well done!
It was a bit confusing at first as it was unclear if me throwing dice at the castles would do anything. So maybe some tiny HP bars above the enemies/structures would be quite helpful.
Didn't see any severe bugs, and the only one that is worth mentioning is that sound seems to stop when you restart the game from the pause menu, and only comes back if you pause and resume the game.
I would definitely add maybe a dice type gun swap, where a d4 shoots 3 smaller d4, d6 is the standard one you already have and maybe a d12 could be a splash type grenade. Cycling through with Right click could work as I don't believe that button is assigned to anything and it could add to the charm.
Also it seems the enemies take a bit to spawn in and it's quite easy to just destroy most of their barracks before they spawn.
It's quite a nice game!