I love the concept. Visuals are nice. I didn't encounter a single bug or glitch. Gameplay is fun.
Difficulty is rather on the easy side - right now it feels like it is pretty easy to eradicate all slimes and then it is only about filling the board with no real threat. But I feel like this is something that can be easily aligned. I also see a lot of potential for this game by adding some more enemy types with different behavior. With some additional content I would happily play it much more.
Very good game.