Breakthrough Hit: The Ren & Stimpy Show, without a doubt. Though considering most of his later work and rumors of how difficult he is to work with, his "breakthrough hit" is also his one-hit wonder.
Creator Backlash: John has actually been pretty critical of his early work, particularly on Mighty Mouse: TNA and Ren and Stimpy. He even warns his fans to not study his cartoons, but rather all of his influences—"For everything I did right, there were a ton of mistakes."
He also refused to give himself credit for his directorial role on the Ren and Stimpy episode Nurse Stimpy. He thought it was so bad that he credited himself as "Raymond Spum" instead, out of embarrassment. He was quoted as saying, "The timing was bad. The drawings are bad. The colors are bad. From an artistic standpoint, to me, it's a really ugly cartoon."
Magnum Opus Dissonance: He's best remembered for Ren and Stimpy, but John considers George Liquor to be his "strongest character".
While he's as critical of APC as the next guy, he considers the APC episode "Altruists" to be the best episode of Ren and Stimpy he's ever made. Needlessly to say, the fandom disagrees with him. Hard.
Mean Character Nice Actor: His character Ren is a jerk, but John can be a pretty nice guy in person. That said, some claim he does descend into Jerk Ass territory, such as Billy West, but he does have his defenders and genuine friends.
Schedule Slip: The often-cited reason Nickelodeon fired him from his own show, although the man himself jossed this and insists "Man's Best Friend" was what got him booted off. He also backhanded the claims of not meeting deadlines since Executive Meddling kept forcing him to retool the episodes over and over until they were accepted.
When John was fired, many cartoons he was working on were left on the cutting room floor. It's interesting to think how his career and show would have gone if he hadn't have been fired.
Why Fandom Can't Have Nice Things: John used to host regular AIM chats with the fandom, and post Q&A sessions on certain Ren and Stimpy message boards. Some chats and question sessions went well, at least at first. However, after a large amount of "heckling" and being drowned out with constant clamoring requests of "Do you like this show? What do you think of this show? What's your opinion on anime?", etc. (mostly done for the purpose of troll-baiting his opinionated statements against animated shows he doesn't like) and even moderation not helping matters of people getting somewhat out of hand, he dropped this method of communication altogether. However, he later would created his own self-moderated blog to talk about various subjects and drawing and animated character theories, and does participate in comment discussions there. He has lessened considerably himself from making as many overt statements about cartoons he does not like quite as much, focusing more of his attention on simply praising the inspirations he does admire.