There are very few big budgeted animated movies about colorful fishes in the sea and the threats there - it almost feel like a completely new universe to explore. Even Pixar will have a hard time to top this film filled with many fun moments and visual surprises.
Finding Nemo is for everyone, quite literally in fact, it's in its central theme: parents will relate to Marvin and understand that sometimes is good to stop being so over-protective and let your child go. Children will relate to Nemo in a sense that parenthood might feel like a jail but it's all done for the greater good. Every character is quirky, fun and well written. Ellen DeGeneres made a tremendous job as Dory.
I feel like "Finding Nemo" is to Pixar what "North by Northwest" is to Hitchcock: I wouldn't call it their greatest artistic statement, but it is the film that fully encompasses what they're all about. The animation is positively gorgeous, the humor is excellent, each character is distinct and memorable, and the stories unfold in a way that can resonate strongly with both children and adults.