Decomposing Elements of SpongeBob SquarePantsMany fans believe that SpongeBob SquarePants has had the biggest decline in quality of any show on TV in the 21st century. And while I'm inclined to believe them, let's take a deeper look at how the older SpongeBob (Seasons 1-3) differs from the newer SpongeBob (Seasons 4-whatever number we're on now).
The early SpongeBob, released in 1999, was loved for its humor and nostalgia, keeping the elements we loved from a few 90's shows and putting its own personal SpongeBob twist on them. It was one of the most recognizable works on television, and technically still is. But older SpongeBob also had great stories going on. It had its own personal touch on unique elements such as sponges getting the suds instead of cold, or Goo Lagoon being addressed as a mud puddle instead of an underwater body of water. Basically, the old SpongeBob never forgot that it was underwater, and covered a world that was not human, and did not copy exactly everything that goes on in human society.
Newer SpongeBob, however, tries in a poor way to keep up with what old SpongeBob laid down. In seasons such as five and six, most fans agree that the plots are forced and unfunny. However, in later seasons, such as seven and eight, we see Continuity Nods such as SpongeBob mentioning that he had the suds before, while completely out of context to the situation going on in the episode. Newer episodes of SpongeBob are still trying to keep us hooked on the elements that old SpongeBob already laid down for us, while most fans who still watch the show are trying not to connect old and new SpongeBob. That being said, new SpongeBob does not provide any further connections than the pointless Continuity Nods, in that all the characters have undergone Character Derailment in some way. Even if you don't believe this, many long-term fans of the series can agree that the characters seen in new SpongeBob do not possess the same charm to them that they did in old SpongeBob. Characters such as Mr. Krabs are now expressed in an antagonistic light, and play to the many rundown plot cliches that are expressed in every episode we see them in.
In conclusion, the decline of humorous occurrences in the new SpongeBob has to do with the lack of effort to match the two together in the unique elements and character traits that old SpongeBob already set for us.
Alternative Theory On Show's DeclineAfter the movie, series creator Stephen Hillenburg left, leaving the executive producer position to Mr. Paul Tibbitt, who seems to allow any episode through, no matter how out of character any given character is. Most fans agree that the majority of Season 4 is at least okay, while Seasons 5 and 6 marked a rapid decline in the show's quality, most likely a cause of the show's writers initially not wanting to disgrace the sheer quality that was the first 3 seasons.
Late in Season 4, of which the first half contains some continuity nods that were done with SOME respect (there were some plot holes such as Ol' Reliable returning, despite Patrick having broken it in "Nature Pants), more creative reign was allowed, and flanderization ensued. After the particularly harsh backlash against Season 6, Seasons 7 and 8 have been a bit of a return to form, with some episodes, such as "Treats!, surprising their fandom as the humor is genuinely funny at times and the flanderization isn't as noticeable. The show's writers have noticed the show's decline and have publicly said that they're trying new writing combinations to see what works and what doesn't.
Concluding on a somewhat bitter note, a large portion of the episodes have still been crap, however, and some members of the fandom argue that no matter how much better the show gets, it will still live in infamy due to Seasons 4-7.
Stephen Hillenburg is returning for Season 10, and Paul Tibbitt is being replaced as showrunner.