The Olaf short was actually pretty cute. Granted, it went on for far too long in my opinion (30 minutes roughly) it had some funny jokes about how twisted a lot of Christmas traditions are (hanging stockings over a fire, decorating the corpse of a tree, and at least 4 fruit cake jokes). It wasn’t bad overall, but it certainly shouldn’t have been in front of a Pixar movie.
As for Coco itself, I thought it was pretty great. Some similar concepts from the Book of Life but nothing that seems like it’s a blatant copy either aside from Musician, and that both take place on Día de los Muertos. The animation was fantastic as usual for a Pixar product, the songs and characters were fun, and the film brought in some nice twists in it as well.