This one is hard to rate... I almost always check out new cartoons, and occasionally there are hidden gems among the general muck... such as "Steven Universe". With this show, I hardly can fathom how to rate it and I had to force myself to watch 3 episodes. It wasn't awful, but it wasn't anything that interesting either. But I think I know why, and it's two main factors. And I think that's also why despite this series garnering over a hundred million views, there are virtually no critical ratings or analyses.
Firstly because it's CLEARLY not for anyone over the age of 6. I got absolutely nothing out of it. The story and character development is incredibly basic, hyper-simplified so that toddlers can comprehend it.
Secondly, it's very VERY odd. Almost "Teletubbies"-level odd, but slightly more comprehensible. The world is somewhat reminiscent of "The Little Prince" in its construction of many small moons with different traits and inhabitants, but the story has an anime-like feel... I would say something along the lines of almost a "Samurai Jack" for 3-year olds... and the sum effect of anyone old enough to form complete thoughts watching it boils down to 'wut?'. I can see how very young children overall would be hooked by it. It has all the flashy colors and quick movement that keep little kids... and cats... fixated.
So, I suppose this is the equivalent of having your kids chase a laser pointer dot on the floor. But it's not really an entertaining cartoon for anyone really looking for a higher level of story or characters or humor. You could view it as a competent introduction of story elements, but I really don't think it's going to have much staying power. I predict something of a fad time period which will begin to burn itself out in about 3 more years, much like "Teletubbies".