The first season of Tokyo Ghoul, while certainly not reaching the heights as the manga, was an enjoyable exposition to the series that was able lead newcomers like me to binge read the entire 143 chapter manga in two days. As a stand alone show, ignoring the quality of the manga, it was pretty good.
Root A, however, is trash from an anime-viewer-only perspective and worse than trash if you've read the manga. It is a mess of unexplained plot points that insult the complexity of the source material it was adapted from. For all the hype generated by Sui Ishida creating an original plot line for the anime to follow, Root A fell inconceivably short in almost all areas it could. Studio Pierrot proved itself completely inadequate to handling the franchise and we can only hope that the Tokyo Ghoul series gets the Brotherhood-esque 50-episode reboot with a much better studio.
Despite a promising opening episode that immediately introduced a difference in story to the manga, Root A never seemed to be interested in actually developing an original story. From one episode to the next, content was centered around adaptations of the sidestory in the manga. I never got the feeling that there even was an original element to the story. Kaneki, who should've been the focal point of the so-called "original plot", is left thoroughly underdeveloped and recieves approximately half a minute of air-time per episode. I was excited for the prospect of a different take on perhaps the manga's weakest arc, but found myself disappointed by the lack of attention to the main character. For all intents and purposes, there are zero differences in plot progression between the anime and manga, besides the fact that the anime development of the characters is far inferior. Simply nothing comes of this original direction despite the many glaringly obvious routes it could add to the series. Instead, Root A follows a rather slow-paced development of the supporting cast with intermittent unexplained violence. The story somewhat resembles season 1 Aldnoah Zero - intriguing major plot points outlined but no content to flesh out the story and add impact to the plot's important events.
A large part of the problem is no doubt due to the shortness of the adaptation. The first season, while not perfect, was able to a manage a somewhat coherent story condensing around 60 chapters of manga. Root A attempts to condense something closer to 75-80 chapters and royally screws it up. Major story arcs are melded together so that the overall picture is completely nonsensical. There is no coherent progression from one event to the next; the end result is that the series as a whole feels like a haphazard, condensed jumbling of the manga. With everything feeling rushed and coming from left field, it's nearly impossible to get invested or enjoy the story.
That said, there are some legitimately good scenes of character development of the side characters. Suzaya Juuzou's character and his relationship to Shinohara is actually better done in the anime than the manga. Unfortunately, the rest of these character development scenes are mostly direct adaptations from the manga. If you've read the manga, you will very soon forget that this is supposed to be an original story, as 90% of each episode is cut from the manga. You really begin to question Studio Pierrot's priorities, as the main story arc is so sidelined by side stories (how ironic) that when bouts of action occur, you simply have no idea what the conflict is about. Pacing was an issue in the first season; however, Root A takes poor pacing to a new level.
The major climax of the manga was impactful and well thought out but gets completely butchered in the anime thanks to a missing major fight as well as the larger issue of simply not adapting enough of the main story to really understand Kaneki's profound development as a character, which is what makes the final arc so epic. Once again, I really have to question the director's priorities - if you plan to adapt the epic, final showdown of the main story arc, why wouldn't you spend more time adapting the events of the main story?
Animation-wise, Root A is fairly underwhelming. The art is nothing spectacular (aside from one beautifully detailed keyboard) and the animation hits power-point level quality during some fight scenes. With this show, Studio Pierrot proudly declares to the world that fighting scenes are not their forté and fills most major fights with smoke so nearly all art is obscured.
Sound is a similar story. Pierrot should have kept the same opening song from the first season (Unravel by TK from Ling Tosite Sigure), which will undoubtedly be the most memorable piece of the Pierrot iteration of the franchise. This is pretty evident considering Pierrot even brought in an acoustic version was made specifically for the (rubbish) final episode of the show. The ED is a decent song but the series offers nothing spectacular when it comes to OST aside from the one standout song that came from the first season.
Overall, this was an extremely disappointing follow-up to a semi-decent first season. I'm still having trouble comprehending the stupidity that was the decision to cram the brilliance of the 143 chapters of Tokyo Ghoul into 24 episodes; furthermore, the hint of a :re follow up is nothing more an insult to manga readers. Root A has some good moments of character development, but that is due entirely to a direct adaptation from manga scenes and should not be any way credited to Studio Pierrot. In fact, Root A has only shown that Studio Pierrot should not adapt any more Tokyo Ghoul material - or any material really.
Overall Rating: 5/10
TLDR; Read the manga from chapter 1, watch episode 12 of the first season, avoid all else. Or, wait for the 50-episode remake of Tokyo Ghoul it deserves with a competent studio.