I recently went back to watch some old kids shows with my girlfriend. I have to say, this show is almost as good now as it was when I was a kid. The humor can be outdated at times, and the first season isn't as good as the rest, but all-in-all, this kids show, much like many of the other Cartoon Network / Nickelodeon Animated shows from the early and mid-2000 holds up well and has a very nostalgic feeling to it.
With all that said, there are some negatives. For starters, Cheese. When he is introduced, he works by himself for one or two episodes. But the show took it a little to far every once in a while, throwing in annoying characters that worked for about five seconds before making me wish they were gone. Luckily, the main characters also would get annoyed with them, so it's not that bad.
Some of the episodes are genially great. Some are hit-or-miss, and some are bad. Most TV shows are like this and you can't escape it.
All-in-all, this is a great kids show with some discreet adult humor sprinkled throughout that makes it much easier for adults to watch this. But with that said, most adults (that I know at least, and millennials) could watch this show no problem without the head- banging annoying goofy over-the-top colorful migraine inducing characters and animation that brand new shows have.