Jimmy Neutron is a show I loved for the longest time as a kid, and like a lot of other things, I outgrew it and lost interest in it.
Watching it years later as an adult, it is not a bad show. The animation is not bad, but comparing to other CGI at this time, it is dated and not as good. But what I like about the show is it still has its fun moments and fun episodes. The first season has a lot of good episodes, but I personally feel the show gets better with Season 2 when the plots and the conflicts of the episodes get more intriguing.
I like the majority of the characters. Some characters are a bit odd and zany, but most other characters are good, likable, and funny. It's one of those shows where when you get to know the characters a bit more, you end up liking them and even relate to them.
Jimmy, himself, is a pretty good main character. I like the creative inventions he makes. Sure, his inventions do cause mayhem (wether it's his fault or not), but Jimmy's personality and intelligence is what makes him work really well as a main character, and he isn't annoying either. His dog, Goddard, is awesome and probably my favorite side character of the show.
Even though there are other Nicktoons I prefer, I still like this show. It's not bad and it has aged fairly well.