The Jimmy Neutron TV show that this film spawned kind of lost its marbles towards the end of its run, from what I can remember, but this film is a genuinely solid comedy film for kids and adults alike.
The visual aesthetic of the film, at the beginning, gives it the feeling of a 1950s, cheesy scifi film which, I felt, was a great match for this. There is also a discreet (possible) Star Wars reference which I noticed when I was a kid that I'm still convinced is there.
The animation, I was a bit surprised about. Being a CG animated film from 2001 that wasn't coming from Pixar or Dreamworks, you don't expect animation quality to be very high, yet seeing this film again, I'm impressed with how good it still looks today.
The voice acting is right where it needs to be for a film of this sort. The villain and his henchmen are funny and over-the-top, Judy is a sensible parent, Hugh is her comic foil, and all the kids sound the way they should for a film like this. The interactions sound like all the actors were simultaneously present while they recorded their lines and it is all very cohesive and tonally appropriate.
The writing is surprisingly good. I enjoyed the film well enough as a kid, but all these years later I have only managed to find it more enjoyable- not in the meta, meme sense, but on the film's own terms. Many of the jokes I didn't catch as a kid land for me now, and the ones that did land for me as a kid, have only gotten better. The premise is pretty creative and the execution very efficient. There are some plot cliches in this film that aren't played up for laughs, but they are forgivable. The film's pacing is perfect. There's never a scene that feels like it drags, or scenes that come and go for no reason. Only the necessary things are ever shown and things move along swiftly and steadily, which is great for a kids' film, I think.
Jimmy Neutron: Boy Genius is a well-crafted film. It's not necessarily groundbreaking but it is a fun, solid film that is deserving of repeated viewings.