First impression with the menu was quite nice I must say, really liked the diagetic implementation of it. Though it seemed that it started in the level select screen instead of the main menu?
Nice to see Lemmings-like gameplay, don't see that kind of game often, but there wasn't much of a spin on it and some of the forms felt unresponsive relative to the spawn rate. Some of that unresponsive-feeling could be chalked up to a lack of sound effects for the slimes themselves, but the animations could use some snappier timing as well. The slimes themselves are cute and the transformations are nice, but could benefit from applying some animation principles such as squash & stretch and follow-through.
The level editor is a nice little technical-show inclusion, though I did find it weird how it seemed I couldn't put objects on the main layer in front of background walls, and it would be nice if the game elements that really need collision to work such as the gems could only be selected while you're on the middle layer.