Atlantis had a great first act, but once they actually got to Atlantis I forgot about the great animation, great character designs, and kinda interesting characters and was like "man this sucks." If they had done a better job with the second act the movie wouldn't have been as bad.
And Atlantis, Nadia, and pretty much EVERY SINGLE story that involved deep sea exploration and deep sea civilizations all ripped off 20,000 Leagues Under the Sea, and several other titles that explain how such a civiliation would work.
As far as Lilo and Stitch goes, yes well worth it. It's an amazing movie, and the only one after 2000 that's lived up to the Disney name. It's the only movie from WDFA worth watching that's been made after the end of the Renaissance. Great characters, BEAUTIFUL water-color backgrounds, all around just a great movie.
I actually thought the advertisements were genius. They established who Stitch was, making you love him before you even saw the movie, and also pointed out that this isn't a traditional Disney animated feature. Ironically, it's the only recent one that could be considered a Disney classic years from now.