In case you haven't inferred by the title, Naruto filler is bullshit. If you still watch this show, then you're an idiot. If you plan to start watching this show, then you're also an idiot because this page obviously contains spoilers.
For the first 80 or so episodes, Naruto was one of the most addictive series I had ever seen. Then the producers of the anime realized that they were in danger of catching up to the manga, so they raped the series to slow it down. It went something like this:
Even after the Attack on Konoha story arc, there were still some exciting episodes like the fight between Itachi and Kakashi. Soon afterwards however, the anime added gratuitous bullshit to kill the pacing of the show. Then the Naruto producers spit in the viewers' faces by releasing the shittiest episode in the history of anime.
The "Kakashi's Mask" episode was originally based on a short manga special, but it's more accurate to say that the episode was based on a trainwreck. The subsequent episodes temporarily raised the show's standards, but a creatively new path to achieving shittiness soon appeared: Flashbacks. Each new episode would contain approximately half of the previous episode. When this got old, they inserted original material. Did I say original material? I meant prolonged flashbacks to earlier parts OF THE SAME EPISODE.
Finally, when the producers used up every possible flashback, they were left with only two options:
1. Show some class and suspend the series until the manga completes another story arc.
2. Devote an entire season to abysmal yet profitable filler.
Aside from lackluster animation and no advancement to the plot, each filler episode strives to reach new levels of shittiness by feeding the viewers a dull formulaic plot. They probably have one of these at the studio:
Naruto Filler Plot Generator:
I totally ripped off Maddox's Tom Clancy Plot Generator.
42427 people don't realize that the Naruto Filler Regression Analysis is a hilarious pun