Lilo and Stitch is one of my favourite movies, period, and although mostly of its own merit, but also because of Disney's attempts to venture out into other genres. Part of the reason why I love the movie so much is that it's not much like Disney movies; no contrived romance subplot, no real antagonist, and all of the characters presented are well developed, as opposed to the heavy focus put on Girl A and Guy A, the development typical in Disney movies.
The choice of watercolour and the art style
(based on Chris Sanders's own art style, one of my favourite artists, so it gets extra pointsfor that) give the movie and alien feel, and the Disney artists even had to be trained by the man himself how to draw in his style. Obviously, it's another attempt that Disney to try and seperate this movie from the rest of their movies.
As biased as I may be (and I'm very biased), the movie is a lot funnier, and mature than most Disney movies. The dead-parents angle is also treated in a different way; instead of just being an ass pull and motivation for the main character, it's treated for what it is, a tragedy. It also fleshes the character of Nani out, making her one of the more fleshed out characters in the movie.
All in all, I think the only problem I have with this movie is how much it was meddled. Not that it was neccesarily a bad thing, and pretty much everything left out is in the Extras menu, but I'd just like to see how things would have been otherwise.