The medium in general was considered to be going through one from 2008-2012, when there was a prominent shift towards Lighter and SofterMoe productions that pandered to otakus, with little to no regard towards international appeal. Meanwhile, the rise in fansubs and illegal torrenting discouraged dubbing companies from producing dubs for foreign audiences, who could easily download a fansubbed anime episode just hours after its Japanese airing for free. During this time, it became more popular to mock anime fans than to be one, with the Kawaiiko and Occidental Otaku stereotypes becoming common insults against them. The age ended around 2012 or so, since the airing of several well-received, non-moe anime in the following years and the revival of Toonami have spurred a renewed interest in anime & manga in the west and a gradually re-emerging interest in international appeal in the east (for instance, Toei Animation decided to uncancelDragon Ball Kai as a result of the anime's wide appeal in the west).
Astro Boy might be a classic, but not even it is immune to dork ages. In the sixties, Tezuka had Astro Boy go through a Face–Heel Turn, and wrote a story where a construction error turned Astro Boy evil. Instead of being a champion of justice who never wanted to hurt a human being, the evil Astro didn't care a bit about human lives anymore. Though Tezuka was fully aware that violent anti-heroes were the latest trend in manga, he didn't feel that it was the way to go for Astro Boy, but his editor insisted that an Astro Boy who killed people and destroyed buildings would be more interesting. Tezuka himself was convinced that the readers preferred Astro to be a good-hearted robot, and was proven right when the readers turned out to have zero interest in reading about an evil Astro Boy. Tezuka changed him back, but it took a lot of time and effort to get the series' popularity back.
Once Reiko Yoshida left the Tokyo Mew Mew project, Mia Ikumi tried to write a sequel incorporating the retcons made in the TV show and replacing Ichigo with a new character named Berii. Ichigo herself lost her powers except as a living accessory to the new heroine, her origins and family life were completely ignored in favor of sending her to Europe, and she became a washed-up hero. It's no surprise Tokyo Mew Mew a la mode has a high degree of Fanon Discontinuity amongst fans who also really dislike Berii. Berii herself has been Mis-blamed, though; the real blame lies in the publishers, who, among other things, restricted the series to just two volumes when commissioning the sequel.
Many, many fans of Dragon Ball see Dragon Ball GT as this. After the end of Dragon Ball Z, Toei Animation decided to bank off of Z 's success by creating an original sequel series taking place after Goku leaves to train Uub. The anime attempted to return the franchise to the comedic roots of the original Dragon Ball, but suddenly went back to Z 's Darker and Edgier tone after Toei realized how little people appreciated the comedy. Many of GT's detractors state that both the comedy and drama of the show was shoehorned in compared to the more natural flow of the original manga, and the sudden shifts in tone taken by GT certainly didn't help matters. Despite Dragon Ball creator Akira Toriyama giving his personal approval of the series, it's become so disliked that one of the biggest points of debate in the fandom is whether or not the show is canon. Luckily for these fans, Toei seems to have redeemed themselves with Dragon Ball Z: Battle of Gods, Dragon Ball Z: Resurrection ‘F’, and Dragon Ball Super, which are not only seen as superior sequels to Z, but also seem to ignore GT entirely.
For some portion of the fanbase, Magical Record Lyrical Nanoha FORCE has become this for the main continuity of the franchise. The series became Darker and Edgier, but the method of doing so was introducing an Anti-Magic virus into a magical setting. This led the new villains to become a Villain Sue gang that beat beloved favorites almost insultingly easily while being insufferable, hypocriticaljerkasses, the heroes have to combat them with Flawed Prototype weapons that barely even work and the new main character is, unusually, a heterosexual male that has so far not done anything beneficial for the heroes. Even worse, it has undergone a massive Schedule Slip, releasing only 30 chapters in the four years of its publishing. Perhaps due to all of these reasons, it is currently on (a most likely permanent) hiatus.
While JoJo's Bizarre Adventure is still very popular in Japan and considerably well-loved in the west, each region has their own candidates for the comic's low point:
In Japan, Diamond is Unbreakable is seen as a rather inferior Post-Script Season compared to the first three parts. Reasons for this include the retcons of the bow & arrow and the protagonist Josuke being the illegitimate son of Joseph, the incredibly formulaic Monster of the Week plotline (which had already been established as a formula in Stardust Crusaders), and the lack of a real end goal until Reimi Sugimoto and Yoshikage Kira show up. Not helping is Hirohiko Araki displaying a conspicuous bias in favor of DiU, classifying Josuke as his favorite JoJo and pushing for representation of part 4 to the point where Japanese fans see it as over-represented.
Japanese fans have also expressed their distaste for Stone Ocean, though exactly why that particular part is so loathed is a pretty big Broken Base; all that can be discerned is that for one reason or another, part 6 isn't exactly the most popular part on domestic shores.
Overseas fans of the series tend to look down on Vento Aureo due to the perception of main protagonist Giorno as bland and uninteresting (though translations may be to blame for this), the extremely-formulaic Monster of the Week nature that exacerbated the flaws of the previous two parts' plot styles, the narmily-designed and overly-generic villain Diavolo, and the ending, which reeks of Deus ex Machina even by JoJo standards. Detractors take particular ire towards Giorno, who for the latter reason plus the fact that he's the illegitimate son of DIO (even reappropriating his battle cry of "MUDA MUDA MUDA") comes off as somewhat of a Marty Stu.
Interestingly enough, each of the above parts that is loathed in one region is highly enjoyed in the other.
A sizeable portion of the fanbase felt that Bleach went into a Dork Age with the Fullbringer Arc. The arc focused on new characters with totally new powers instead of the established characters and featured a plot that seemed almost completely unrelated to any part of the Myth Arc. To be fair, with Ichigo depowered and Aizen alive but imprisoned, there weren't many plot threads that could be carried over directly from the previous arc and at least nothing involved Aizen.
There are also fans who consider the four year long Arrancar Arc a Dork Age. In general, the writing became a lot more divisive after the Soul Society arc, and the series' sales and ratings dropped to the point where the anime was cancelled as soon as the Fullbringer Arc wrapped up.
Some renowned studios have also taken big hits. Studio Gainax has lost some key creators like HiroyukiImaishi and Hideaki Anno, who have formed their own studios. As a result, Gainax seems to have decayed from producing acclaimed original series to mediocre adaptations of Shōnen manga such as Medaka Box.
The retirement of Hayao Miyazaki in 2013 sent Studio Ghibli into an existential crisis. But, even before Miyazaki gave up film-making, the studio is considered by its hardcore fans to have entered a Dork Age starting around 2004 when Miyazaki released Howl's Moving Castle, which did well on both sides of the Pacific but got mixed reviews. This was followed by his son Goro's Tales from Earthsea, which was critically-panned (especially by Ursula K. LeGuin) and thrown into No Export for You limbo in North America for several years due to rights issues. After that came Miyazaki's Ponyo, which was a return to the whimsical tone of his late-80s-era movies but still disappointed hardcore fans despite doing quite well at the box office. By 2010, longtime producer Toshio Suzuki openly speculated about closing the studio, although a shutdown was at least delayed by the modest success of Arrietty.
Saint Seiya hit its dork age with Saint Seiya Omega. It's not Kurumada canon, it changed the super-suit from metal armor to spandex, it added a superhero school, the eponymous character is rarely in the spotlight(!), and so on. It seems that the writers eventually understood why it was so hated, and gave it a second season that thoroughly reverted all changes.
Some fans also consider Smile Pretty Cure! this (though it is slightly better regarded) due to its episodic, goofy nature (to the point that it feels more like a spoof of the genre), childish writing (with both the Myth Arc and character growth being non-existent), and what many see as blatant pandering to the Moe crowd. On the other hand it was allegedly very financially successful...though mostly only with otaku. It says something when its first SH Figuarts figure is the Ensemble Darkhorse otaku character (Yayoi/Cure Peace) and not the leader.
Arcs tended to give Kaiba's backstory or company more prominence, and each arc had its own kind of sin for the fans: the Virtual World interrupted Battle City, and was incredibly weird and nonsensical to many people. Waking the Dragons/Doma had irrational characterization for both Yami and Mai, and screwed with the history of the Shadow Games, and the KC Tournament arc was perceived as just a long breather episode that did little even to expand on Kaiba's character, who the Big Bad of that arc was targeting. And that isn't even mentioning the oddness that is Capsule Monsters.
When the people who write the filler arcs have to do their own series, you get the first two seasons of Yu-Gi-Oh! GX. The original series ending and the considerably lower quality of GX's dub did it no favors in the popularity department, but even fans of the series acknowledge that the series's lack of focus, slow pace, and excessive goofiness did a lot to ingrain the "spinoffs are always awful" mindset. That it came directly after one of the most filler-heavy and poorly-animated segments of the original meant that fans tend to label just about everything after Battle City to be a Dork Age. Thankfully, it Grew the Beard with the Yubel arc, rescuing the franchise from its Dork Age in time for the first season of 5Ds.
You also won't find many fans of the first two arcs of the second season of 5D's, which is sometimes considered the weakest point of the franchise. Criticisms include either dropping plot threads from the first season or resolving them in anticlimactic ways, demoting the female characters to extra, an absurd amount of Product Placement, and a gargantuan block of irrelevant filler episodes at the beginning of the season. The season had to be extensively rewrittenfollowing a real-life scandal, namely the discovery that one of season 1's voice actors was a member of the dangerous Roma Sophia cult, under investigation in Japan at the time. In particular, it was required that almost all elements of mysticism be removed from the series, which led to a hasty retconning in of a sci-fi rather than magical origin for the Big Bad Yliaster organization, among other changes.
The 5DsDork Age extended into its successor series, Yu Gi Oh Zexal, which took the childishness, stupid designs, filler, and Recycled Script of the other series and magnified them. Thankfully, it pulled itself together by the introduction of the Arclights and jumped heavily in quality with ZEXAL II, but the back-to-back combo of 5Ds second half and ZEXAL first half was quite the blow to the show's older fanbase.
The second season of the Black Butler anime is seen as this by nearly all of the fandom. The shotacon fanservice was cranked up to intolerably squicky levels, the new characters were poorly written and completely unlikable (and the returning ones were derailed or flanderized), and the plot was a near-complete mess that had nothing to do with the manga and had a Gainax Ending. It took years for another season to be made, and it unsurprisingly ignores everything that happened in this.
Transformers Armada was very rushed, with many bouts of Off Model on par with those seen in Generation 1, an English dub with clunky dialogue, incorrect names and originally silent moments filled with inane chatter and stock phrases, and a slow beginning with repetitive episodic adventures happening before the plot really kicks off. But the main reason why Armada isn't considered the worst Transformers series ever is because Transformers Energon took that spot with almost little competition. All the problems with Armada were amplified, with the plot starting off good, before repeating itself halfway in and having the final few episodes have nothing to do with anything, character arcs largely being quietly dropped or else ended in a way that doesn't actually resolve them, the setting robbing the cast of any real need to transform, and the CG models lacking emotion (to the point where sometimes they're hand-drawn just because it looks more impressive). The dub is even worse - unfinished animation is used, Lull Destruction is in full effect (seriously, count how many times you hear "Uhh?" in a moment of silence), mistranslations are plentiful, and an important episode that develops two characters is dropped and replaced with a non-canon Japanese special. Just read whatTFWiki.net has to say about it.
Transformers Cybertron is, however, agreed to be a massive improvement over its predecessors (with the dub and animation being far less shoddy than them), though it still has its flaws (such as an abundance of Stock Footage used to pad episodes, and a drawn-out first half with a comparatively trunciated second half).
Pokémon: You'll get a lot of answers for what counts as the show's Dork Age (and if it has ever left it). Two examples crop up more often than others: Johto and Unova.
Johto is a common citation as it contains the start of the fall of Team Rocket, Brock and Misty being reduced to moving background, flanderization of the main cast, and the "Filler Hell" in general. While it started within Season 3 (with the GS Ball becoming an Aborted Arc and such), it is Season 4 where the reputation for Johto comes from: very little of significance takes place (no captures, only several evolutions and three very spaced-out badges), and the filler was less memorable overall - the slower pacing led to much of the old vanguard becoming disillusioned with the show. That said, the succeeding "Master Quest" season is largely considered a return to form: more development of the show's Myth Arc, more Story Arcs to spice up the plot, stronger standalone episodes, and wrapping up the Original Series with a solid Tournament Arc (the Silver Conference being a Tough Act to Follow judging from the overall response to later League arcs) makes people more forgiving of it compared to what Johto previously gave them.