What a well put together game! I'm jealous of your art skills. Looks and sounds great and very playable!
I got through level 11. I found myself wanting to be able to upgrade the AoE of the sunbeam, in later levels it got a little tedious having to hit them exactly. Particularly because I was finding more and more that I was not able to be hit from any direction.
Once the levels progressed, I found that I had to stick to just the immediate goblins around me until I was able to get those slimes cleared. By that time, all the other goblins were sad. Maybe having the slimes come in waves would allow the player to juggle keeping more goblins happy.
Overall, great job!