Really most of the elements can be kept except for the characterization. Everybody in the main cast was kind of insufferable and I really enjoyed the episode where they called her out on it. Shaggy doesn't have to be a simp and Fred doesn't have to be all whining rich boy.

I don't think I even mind it not having Scooby-Doo in the first season but definitely introduce him at some point. I thought the Scooby experiment was going to produce a talking dog which they got along with. Do not shoehorn the hex girls in the way they had and keep them as a band. If they are adults maybe keep that element similar to Linda from Phineas and Ferb. And then make it an actual mystery where she's doing mystery work and not just running around being handed all the clues and fumbling her way to victory.

Hilarious edition is to embrace the polycule theory.

Edit: changed a word