Simple but nice concept that fits the theme well. Reroll mechanic adds some basic strategy. Cute graphics and sounds. The main problem is it's very short, but that's to be expected given the time constraint.
If you do decide to continue work, I recommend targeting mobile platforms. Adding more gameplay mechanics (even simple RPG systems, like an exp bar or stat upgrades) would go a long way. Also bumping the difficulty down to 1 slime instead of 2 for the first encounter, and making the gameplay faster (faster animations, etc) would be great.
My game is pretty similar, you should check it out.