I've never liked Ren and Stimpy. Bleh!
If I remember correctly the finger cats episode was a reference to the anime Akira. I've never actually seen it, but I'm pretty sure the creator is a fan of anime so it would make sense. It was a little strange I'll admit.
It is random and silly at times, but it's no where near the randomness/stupidity of some shows (like Ren and Stimpy and Regular Show). I think it gets some of its charm from the silliness. Some things tend to make more sense in context than out of it. Like the cat fingers for example. The main four are magic entities that can shape shift, so Steven decides to try it out. He's never done it before so he is only able to shape shift his fingers, and it ends up getting out of control. (It still sounds kinda wierd now that I'm typing it out

)
I'd say it's as silly as the better episodes of Adventure Time like the gender bent episodes (which Rebecca wrote), but it gets a bit serious sort of like the Marceline and Ice King episodes (which she also wrote). If you aren't too familiar with those you could also compare it to the Powerpuff Girls where a lot of it was pretty silly, but it wasn't overkill. There are some songs in it (again think Adventure Time), but they're not like big musical numbers. It's mostly just Steven (he sings a little jingle on the way to get some pizza, etc).
In terms of humor, the creator stated "It doesn't have to be cruel to be funny", so there isn't like immense amounts of toilet humor and what not. (Which I love because toilet humor is one of the worst forms of humor I can think of).
It definitely gets better as you go along (though my least favorite episode is "Frybo". It got pretty strange...) I'd say whether or not you enjoy the silliness and humor is just a matter of personal preference. I personally think it's pretty cute.