Pixar itself has undergone this as it has grown more skilled at averting Uncanny Valley and No Flow in CGI. This is especially noticeable when you compare the look of the Toy Story characters from movie to movie.
In the first Cars film, Lightning McQueen is depicted with a pair of large stickers on his front bumper that resemble fake headlights (hence his nickname, "Stickers", from his girlfriend Sally). In the sequel, for some reason has his fake "headlights" replaced with real ones, and has remained that way ever since (calling him "Stickers" would now be pointless since he has real headlights now). Also, in the first film, all of the background cars are clearly based on completely fictional models, while in the sequel, all of them are now based on real models.
Wallace & Gromit look very different in their first short, A Grand Day Out, which was effectively a glorified student film. Wallace, in particular, lacked his characteristic wide-mouthed grin (except while saying "cheese"), and Gromit looked rather anemic. Also, the modelling and production were rather more rough-and-ready. The designs (and production methods) were greatly refined in their next film, The Wrong Trousers, and have remained that way ever since.
A curious example, but take a look at Piglet's one-second appearance in the original intro song of The Many Adventures of Winnie the Pooh (the "there's Rabbit, and Piglet, and there's Owl" part). Someone at Disney must have done some heavy redesigning before Piglet made his "official" animated debut in the second featurette.
Combining this with Technology Marches On, try watching the first Shrek after watching Shrek Forever After. Three films' worth of subtle CGI improvement become immediately apparent.
The Astérix movies animation gets better with each installment, for example Asterix the Gaul was animated in an early 60's Hanna-Barbera/UPA cartoon style while Asterix Versus Caesar uses a style reminiscent of Disney theatrical films.
Godzilla has had numerous changes made to his appearance over the years, with newer designs often bringing back elements of older designs that had been abandoned.
Godzilla Final Wars shrunk his eyes and made his body more compact to facilitate the elaborate fight scenes.
Godzilla has once again had his design updated in Godzilla (2014). The most noticeable changes are gills on his neck, round, sauropod-like feet, and a much longer tail. The film crew also spent quite a while tweaking his face:
Edwards:"Trying to get the face right was the main thing... I guess he's got more of a bear's face, or a dog's. We also used eagle. There's a lot of nobility in an eagle. It made him feel very majestic and noble"