I was usually more of a Cartoon Network kid than a Nick kid, but yes, HEY ARNOLD! was one of the Nicktoons that I did actually enjoy very much.
When one thinks about it, Arnold had a way of subtly dealing with certain topics that were otherwise kind of heavy for regular kids shows... I mean heck, just look at the Patakis: you've got a workaholic father, an alcoholic mother, an older sister who was doted on, and a younger sister who was neglected.
On the note of the Jungle Movie being canceled, did you know that a spin-off series was in the works, but never materialized? It was going to focus on Helga and her family, and was supposedly going to be a little more edgy and less sugar-coated than in the original series (like, I believe, they were going to straight up acknowledge her mother was an alcoholic, rather than using euphenisms that kids wouldn't pick up on).