Fun take on the theme, reminds me a bit of Dungeon Keeper! Music and SFX were great, graphics were simple, but readable and fitted the overall style very well. 

As far as strategy goes, I found myself spamming spikes as they seemed to work a lot better than archers, perhaps some adjustments to the level design to give more reason for the archers? Obviously it's a gamejam so time is limited, but having additional upgrades or stronger enemies as the game progressed would have added a lot (I only played for a few minutes, so I apologise if these do exist and I just didn't reach them).

I think the game has a really solid concept and just needs a bit of tweaking with balance to make it great!

-Greg