Well, it's a slime, that's for sure!
Overall I find it a bit fun to play as. It takes a bit of practice to try and master this little guy's abilities, but you'll soon be balling in no time. With how capable the little guy is, you can probably even traverse certain character's paths with enough brute force.
There's still quite a bit I have not seen as I have not finished the campaign with Slime, but I'm sure that there's plenty to be seen and enjoyed with friends. If the single player campaign is fun, then it's probably even better in multiplayer!
Despite the small amount of sprites, it still feels very expressive and alive. There's very good usage of squash and stretch in it. Plenty of it.
This review may be a bit biased since I like slimes. It's okay though. Very fun, yes yes.