Next Dimension, started in april 2006, is the sequel and also the official prequel to Saint Seiya, as it was designed by Masami Kurumada himself, the original author.
The story takes place immediately after Hades, retoning Seiya's death (which occurred at the end of the classic manga), changing it to a momentary "coma". Saori Kido and the other protagonists, to save his life, will travel into the past (thanks to Chronos, the primordial of time, not the king of the titans of Ep G), at the time of the previous holy war (240 years before), to destroy Hades's sword. This is the premise.
Curiously, it is that Next Dimension and The Lost Canvas (a spin-off manga written by Shiori Teshirogi) speak of the same holy war, and have in common Shion and Dohko as young, as well as Tenma (the Pegasus of 700) and Alone (avatar of Hades of the 700).
This was a choice of Kurumada or Shiori herself, because even The Lost Canvas began in 2006, a couple of months after ND (in September). Obviously, in common there are only the names of these 4 characters, the others, and the development of the story, are completely different.
That said, also because the author has carried out other projects over time, the pace of publication of this manga has been (and still is) extremely slow. Generally 7 chapters come out each year, in 13 years 95 chapters have been released so far.
Now the review begins, there could be spoilers.
Summing up in one word, I would say "12 HOUSES", that's ND.
Of course, each series of SS has its 12 houses, but generally only once. Here, in almost 100 chapters, there has been practically only a continuous ascent or descent to the 12 houses, with half clashes between allies.
Moreover, it seems that the author has forgotten the premise, and with this slowness, who knows if he will be able to complete the story in a decent way.
1) The first 20 or so chapters have 3 premises: save Seiya's life (the reason why Saori and the other 4 bronzes go to the past), to tell of the previous war with Hades, and finally sets the stage for a war with Zeus and Olympus.
So, what? The first one is in progress, and there is some alternative solution, because Hades (in 700) seems something unattainable.
2) The second is truly dispersed. From the premise of the first 10 chapters, Tenma and Alone, two friends, had to play an important role, like Pegasus and Hades, in the story of the holy war. In these 100 chapters, the real war is not even started, there were no clashes with the very relevant specters, Alone / Hades has disappeared from the beginning, while Tenma is useless. If you think about it, classic bronzes progressed and got stronger as they got silver, gold and beyond. Tenma here is useless, a normal bronze, scarce, stupid and a copy of Seiya, but that (from the premise) should fight Hades. But in what world?
But apart from that, the war with Hades itself seems to have gone into the background, since the author decided to include the tredecesimo gold saint, Ophiuchus, and started to run the whole story around him. And it is still continuing on this.
Fortunately, Teshirogi, with his alternative story, did an excellent job. So far it is a disaster.
3) The war with Olympus is a saga long dreamed by fans. The problem is that first Kurumada should end the 700's past (and as mentioned before, the war with Hades has not even started), and the manga goes on very slowly, 7 chapters a year. And let's add that the author wastes time with flashbacks on gold saints, nice but avoidable.
We will never see it.
To all this there are added problems of internal coherence (the author creates mysteries or situations, and years and volumes later, solves them inconsistently). An example, the Gemini's true nature.
The manga is full color, the color has changed over the years, the first phase (1-2 volumes) was too saturated, the second (2-9) was good, the third (10-in-progress) has simple tones and few shades shadows.
The design style has remained similar, sometimes better, but less impressive. The historical manga was more particular, paradoxically.
Excluding the classic characters, which are a little disappointing here, there are a couple of interesting, or at least good, new characters. Cancer Deathtoll, Virgo Shijima, Ophiuchus Odysseus, or even Suikyo.
The problem is the others. Or are COPIES of classic characters (Ox is a more stupid Aldebaran, Cain is identically to Saga but stronger, Kaiser is an Aiolia 2.0, etc ...) or they are circus phenomena. I'm not kidding, the author enjoys making them bizarre, even with absurd things (to name one, Gestlat, a sagittarius).
Finally the disappointments. Tenma and Alone, presumed principal actors of the holy war of the 700 from the premise, one totally useless, the other disappeared.
But let's not forget Dohko and Shion. Some of you will remember the classic Hades bow, with some reference to the past war. They 2, renowned veterans, survived it.
Here were two bronzes, promoted to gold. They do not shine in any aspect, they are not strong, they are not clever, they have no great charisma, and so far they are not heroic. A total disappointment, one really wonders how they managed to survive.
History makes itself read, simple. As already mentioned, some interesting points are there, or some ideas for the future, the problem is that the author is slow both as publications and narratively (deviating from the theme and wasting time).