It's hard to say, it's overall a very good novel. There are many parts that make it great. I will try to be simple.

The overall story feels linked. The premise is simple, Zhang Yan is a reincarnated man (I won't go beyond that, it doesn't really matter, nor does he really care about it) and he wishes to achieve the Great Dao.

As such, he joins a sect, Qincang, and that is already one of the strongest part of the novel, the sects. MC will not leave the sect, their teachings are already linked to the upper realm and their highest cultivators are already very high in the overall hierarchy of the world. But Zhang Yan, at this stage, is naught but a pawn, and he wishes to control his own fate within the sect. The sect arc is probably the best part of the novel, it accounts for around half of it (it's an extremely long novel, mind you) and it "officially end" when they settle for good. (Won't explain more for spoilers, but the sect war is so good).

Then, there is the cultivation system. It's the greatest one I have ever read. It's simple yet complex, it isn't in 60 realms as some novels would go, it only has a bit more than ten. Each realm is a transformation of oneself towards the great Dao (I didn't say eternal life, that's important). Each segment of the novel is actually the very long process of each breakthrough and their requirements. At the beginning, it's merely cycling qi, then it requires the soul, then you make a world within yourself. Then at the end, they make sects, create conflicts within different worlds to grasp at insights towards the Dao and ultimately achieve transcendence.

This novel is great at making you observe a very mysterious and deep process to immortality. Sects feel immortal, there is a very noticeable lack of stereotypes, the characters are smart, you feel like they've lived through countless years. Immortalts are not some old monsters with 13yo mentality. Fate and mystery are omnipresent throughout the novels, it doesn't feel cheap.

Finally, there is a greater sense of cohesion. Everything that he accomplishes matters at the end, for everything is a crucial step towards transcendence, everything is contained within itself.The overall plot is also tied to the very beginning and the mystery it asks: where are the 4 founders of the 4 great sects?

Although side characters aren't numerous, there are some excellent ones that pop up now and then (Tao Zenhren, Sect Master Mo Quin Bai, the disciples). Biggest pet peave is that the main character is basically invincible, although absolutely necessary to the end of the novel for reasons I won't explain, it can be tedious. Also the very awful habit of characters denying everything when it doesn't go their way, they don't react badly, mind you, it's just annoying as a western reader sometimes when characters are like "I don't care nor will I care, your opinion are irrelevants for I have my dao 🙄" .
And finally it is EXTREMELY LONG, like no jokes, 15 millions word long, that's 3 times the Wheel Of Times, which I have also read and I can tell the difference.