I've never seen Gravity falls before but I have seen it mentioned a lot on Cartoon Brew and Tumblr. I thought I'd watch an episode or two on watchcarloononline.com, so I chose season 2 episode 1 and 2. The animation is cartoonish and looks like it is designed for a younger audience, with vibrant, bright colours. I love the aesthetic and the character design! It reminds me of the Simpsons or Fairly Odd Parents. The expressions and characters' movements are exaggerated and the story is fantastical to match. I don't see many examples of stretch and squash, and the characters don't have completely realistic weight.
The charcters are super cute, as the two main protagonists are young twins with wide eyes and large heads. The voices are pretty cute too, with the girl voiced by the same person as Louise from Bob's Burgers.
The one criticism I might have is that the style of the show is a little too 'cute' and child-like for the story line and themes, which tend to be a bit more adult and scary.