It totally depends on which era we are referring to. For one, I can say that I love the art direction of a lot of the older films, which includes the Headless Horseman from the second part of Ichabod and Mr. Toad (1949), or how I personally find the style of Snow White an the Seven Dwarfs (1937) appealing, and even Fantasia (1940) (and to be honest, it is that good, and wouldn't mind seeing it again in some format).
As for the modern Disney Animation Studios, there was a bit of a transition when they started doing 3D computer animation, straying far away from hand-drawn animation, seeing that Princess and the Frog (2009) was the last of such. Chicken Little (2005) was a low-point for the studio, seeing how it was disliked by critics, but then they started to release good film after good film, which kind of started with Tangled (2010).
My personal favorites would have to be Zootopia (2016), Mulan (1998), Wreck-It-Ralph (2012), The Emperor's New Groove (2000), and the aforementioned Tangled.