It's the writers and voice actors
that makes Spongebob Squarepants the super excellent show that it is. The animators too.
Stephen Hillenburg, the creator, is actually a marine biologist by education and it was from there that he got the idea of making a cartoon about microscopic marine life.
The issues presented in the cartoons are all quite relevant to kids and grown ups alike. A few that I can remember are: Learning to drive, keeping a secret, procrastinating and busying oneself with other stuff instead of writing your paper that is due in eight hours, living up to society's expectations, forming your own identity, being macho, friendship and loyalty, and even learning to tie one's shoelaces.
The crew that makes the cartoon must be pretty cool too, once they let Pantera guest and play the music for an episode. Definitely, Spongebob Squarepants will be among the list of cartoons I will allow my kids* to watch. And it's a very short list, others in there are Aeon Flux, The Head, Beavis and Butthead, and of course The Simpsons.
* - As of press time, Karf has no kids yet.