Spirited Away is an absolute must when talking about 2000s animated films that hold up. The attention to detail in the animation by Studio Ghibli and Hayao Miyazaki's masterful storytelling still resonates deeply today. Plus, with themes of identity and environmentalism, it feels more relevant than ever.
On the other hand, if you're looking for an underrated gem, I'd recommend the French film The Triplets of Belleville. Its unique art style and almost non-verbal storytelling are so beautifully crafted that they create a timeless experience. The way it mixes jazz music with animation is just magical.
What other themes or visual styles are you looking for in your rewatch?