Berserk is a series that has grown in popularity to be one of the most hailed works within the medium of manga, and for good reason. It's medieval setting, complex character writing, ties to several philosophical schools of thought such as the idea of Nietzsche's Ubermensch and it's top tier art are all factors in why many cite it as the greatest manga of all time.

However, that is a very questionable statement when it comes to analysing the series. Indeed, the quality of the Golden Age Arc, featuring some of the best character chemistry and complexity in the medium through it's main trio of Guts, Griffith and Casca that leads to a story that had many twists and turns as we see knights presented as nowhere near virtuous much like in the hit series Game of Thrones or see characters make complex moral decisions. However, even this isn't a perfect arc, since the existence of the Black Swordsman Arc beforehand spoils what the overall outcome for Guts and Griffith would be, not to mention that even with the level of torment Guts went through, the cruel and almost edgy nature of his character in the Black Swordsman Arc is a notable step down in quality.

Unfortunately, the quality of the writing after the Golden Age is a slow decline. The Lost Children and Tower Arcs were still good in helping develop Guts' character and Serpico makes for an excellent character during his introduction due to his parallels to Griffith. However, the returning cast become far less interesting and the new additions to Guts' group are nowhere near as interesting as the original Band of the Hawk. Casca becomes more potato than character for many, many years of publication and Griffith loses all layers and elegance to his actions to become an irredeemable villain. As for the new cast, Farnese is a typical tsundere, Isidro is a typical child prodigy, Schierke is a loli plot device and Puck, whilst starting out as a decent support character, quickly becomes a bland comic relief.
Speaking of comic relief, the overabundance of this in later arcs lead to some areas of tonal whiplash. A series in which the world is a dark, depressing place filled with murderers, rapists and demons isn't one for chibi deformation gags. If you're one of the people who found FMA:B's comedic scenes a bit too inconsistent, then you'll hate the comedic tone within Berserk's later arcs. On the subject of tone, it also doesn't help that a lot of the action and plot choices that happen feel less like the mature arcs that preceded it and more akin to a typical Shonen. This is present primarily in the Berserker armour being a typical double edged sword transformation that never has major repercussions on the friends of it's user and the "Berserker" factor of it is completely removed in the Sea God Arc.
It doesn't help that in the current events of the series, the pace completely slows down in the current arc even when not taking into account publication schedules, with many chapters feeling unessential and several plot points being dragged out to an unsatisfactory conclusion.

Still, the series manages to hold a lot of incredible merits. The characters of Guts and Griffith are some of the most interesting, well developed characters in the medium that make a very effective duo. The dark fantasy elements remain incredibly cool throughout and the explicit content is enough to draw in those who enjoy gore whilst also having enough substance that it isn't edgy. Moreover, the art is some of the most unique and detailed work within any manga as with the exception of the chibi scenes, each panel is filled to the brim with detail and amazing style.

So, saying all that, is Berserk as good as most say it is? Most likely not, since the quality of the series goes on the decline after reaching it's peak. Despite that, it's not in any manner a bad series, as what it accomplished well it did fantastically and even with it's flaws it's still by far the best fantasy manga out there. It isn't the best manga out there since it's a series that has long since passed it's peak and lost the consistency of it's quality, but it's highlights are great enough to make it a decent contender for that position and still a worthy addition to anyone's top 10.

Overall ranking - 8/10