I will say that the 60s Spider-Man and Fantastic Four cartoons did come very close to capturing the spirit of the comics.
I don't know about the FF cartoon, but I definitely disagree about the '60s Spidey cartoon. It had the action of the comics, but left out the characterization, personal drama, and serialized plotting -- the very things Stan Lee added to comic-book storytelling that were so revolutionary and defined the Marvel approach. I don't think we got any Marvel cartoons that captured those aspects of Marvel's writing until the FOX X-Men
cartoons of the '90s. Those shows, especially the latter, captured the mix of qualities that characterized Lee's writing for better or worse: believable characterization and elaborate personal melodrama combined with wild, bizarre fantasy concepts and intensely corny dialogue.