Mystery Incorperated remains my favorite Scooby show ever.
With that said, I've watched the first two episodes of Velma and I enjoyed them. The mature content seems to mock other 'adult' takes on children's characters, I especially thought the shower monologue regarding sex and nudity to be hilarious. (and fairly accurate) The "gore" is so cartoonized that it really isn't scary, more what you'd expect to see in a cartoon with the brain being removed leaving a clean hole in the skull.
It makes fun of a lot of stereotypes and, for me, that humor hit. I also like the different take on the characters. Norville (not Shaggy) is vehemently anti drug. Fred is a half developed pretty boy struggling under the weight of an overbearing father. While Daphne is still the pretty girl, they're opening up her character in a very different way. And Velma is a teen girl struggling with unrequited crushes, overbearing feelings, and a drive to stand out.
Don't listen to the neckbeards screaming into the nether about the "purity" of the Scooby franchise or their misplaced hatred of Mindy Kaling. Judge for yourself. No, the humor isn't going to hit with everyone, but this feels almost Venture Brothers esque, although perhaps a touch more heavy handed. I like that kind of humor.
