I think that, as far as cartoons go in the last 15 years, Arnold is the cream of the crop, both in values and in entertainment. The characters are a bit wacky (Take Arnold's grandma as exhibit A), but in no ways are they nonsensical. The stories deal with real, pressing issues like disputes between friends, peir manipulation, crushes, and more serious issues like addiction (It's just chocolate!), dysfunctional families, war torn families, even alcoholism and adult illiteracy. All this in an easy to understand fashion that will entertain kids and adults.
The main character, Arnold, is a cultured, empathetic, level headed kid, who isn't afraid to help someone in need. He serves as an admirable role model, to all the characters in the show, who are also admirable and relatable in their own ways.
Now, the show is not without its blemishes. There is some language used, like "crap", and "crapola". And Helga, one of the shows central characters, deals with her unrequited love and family issues by tormenting other children. (Deep inside though, she really has a well meaning heart) But these marginal moments are mild and occasional.
Are the characters regular? Not quite
Is the story all clean pressed? Heck no.
Is it realistic and worth viewing for your kids AND yourself? You bet the barn it is!
The reality we must deal with is that nobody fits into a perfect mould. We're not barbie dolls. Nor is the world a perfect little place. I can't speak for everybody here, but if I was a parent, I would rather have my children watch this little jewel rather than the meaningless, modern day fiascos that air on Nickelodeon these days. And I, for one, will happily join them.