A really cool idea! I could see myself playing this sort of game if it was fleshed out. Some things it would be cool to see:
- defender stamina - perhaps depleted by adventurers, or through a few uses. At zero stamina they could "break", presenting a risk/reward scenario
- in addition to the above if there was an indicator of what adventurers were coming into the dungeon before placing defenders, more careful thought could be placed into which and how many are used
- a feature to "redeploy last defence" for a faster game loop
- "auto-sell"
- an expanded shop
Overall a great job I thought, I really enjoyed playing :)