Without diving into the original Manga source, viewers will miss out on the full enjoyment of these Anime series.
Most of the popular anime series we know today are adaptations from manga. Among them, quite a few anime series have sparked controversy due to significant deviations from the original manga content. As a result, these anime series become hard to grasp and lack appeal for viewers who haven't read the manga beforehand.
1. Pandora Hearts
Pandora Hearts by Mochizuki tells a tragic story that has brought tears to the eyes of many fans. Set in the Victorian era, the story revolves around Oz Vessalius, who accidentally falls into the mysterious dimension called Abyss and forms a pact with one of the monsters there to find a way to escape.

The anime adaptation of Pandora Hearts failed to fully capture the vastness and intricate plot of the series. The Pandora Hearts anime only delivers surface-level details and is forced to conclude with a confusing and unsatisfying ending. Fans of this series are still anticipating a more comprehensive and detailed adaptation faithful to the beloved manga.
2. Tokyo Ghoul
Tokyo Ghoul stands among the anime adaptations notorious for being poorly executed, despite achieving certain successes. The main character, Ken Kaneki, undergoes a transformation into a Ghoul, a creature that can only consume human flesh, leading to a dramatically unresolved story for manga enthusiasts.

While the first season of Tokyo Ghoul still garnered enthusiastic anticipation from fans, subsequent parts fell short. The anime's plot gradually diverges from the original manga, altering many events and characters to the extent that manga fans find themselves confused and disappointed.
3. Gantz
Gantz's brutal storyline has earned it a fanbase for its uniqueness and intensity. The manga revolves around a group of people resurrected by a mysterious force after death. Now, they are compelled to participate in a violent 'game' aimed at exterminating extraterrestrial beings, even if it means trading their own lives.

Gantz's immense potential was squandered during the adaptation process. The anime overwhelms with dense, rushed plot points, focusing primarily on shock-inducing action, violence, and gore, instead of highlighting Gantz's compelling setting or characters.
4. Berserk
The manga Berserk has garnered countless praises from critics and fans alike over the decades. Its captivating dark fantasy setting, coupled with compelling characters, has created an unforgettable masterpiece. However, Berserk has yet to receive an anime adaptation worthy of the author Miura Kentaro's reputation and talent.

The 1997 anime adaptation successfully conveyed Berserk's storyline but ended abruptly, leaving many details untouched. Years later, in 2016, another attempt was made, receiving more criticism than acclaim. Adapting not only the plot but also the visual elements and artwork of Berserk proved challenging for any anime.
5. Blame!
The sci-fi manga Blame! garnered a substantial fanbase upon its release. Despite its minimal dialogue, Killy's dark journey through the vast maze of The City exudes extraordinary allure. Similar to Berserk, Blame! leans heavily on artistic and visual elements, making it challenging to translate into an anime format.

Netflix's 2017 anime adaptation wasted the potential of this manga by amalgamating various story arcs from Blame! This approach left viewers perplexed, often not understanding what they were watching, especially if they hadn't read the original manga.
6. Battle Angel Alita
Battle Angel Alita, a renowned cyberpunk manga in both Japan and abroad, still lacks exceptional adaptations. Despite the resounding success of the manga, Alita's creator, Yukito Kishiro, has no intention of turning the series into an anime or any other form of adaptation.

The 1993 two-episode OVA based on the manga was not the author's top priority. The OVA only adapts a short part from the second volume of the manga, with certain changes for better fit. As an independent work, Battle Angel OVA holds little significance. Whether discovering Battle Angel Alita through the OVA or the 2019 film by director Robert Rodriguez, audiences still need to turn to the manga for a deeper understanding of this series.
