I agree with the general consensus. The production does not feel new or fresh and is not a step forward for C-ent.
However it is still as good and pleasurable to watch as any of the Xianxias out there. As such, if you like Xianxias, it is worth watching for another good experience. If you have never watched Xianxias before, then it is worth watching as it incorporates all of the elements that make xianxias popular. On top of that, it features a talented team that is highly experienced and at the top of their game. Both leads are Xianxia veterans known not so much for their looks as their acting skills - and they don't disappoint. It really seems that they are at the point of their careers where their acting skills have long matured and their charisma shines on the screen. The scriptwriter/director/and art directors also all have plenty of successful productions of the genre under their belt. As such, each scene is familiar but pleasurable to watch. I can somehow imagine showing these scenes in film school as an agglomeration of almost a decade of Xianxias.

Story:
The story is not new and definitely a bit draggy. The ending also feels a bit forced -although somewhat inevitable if one is to truly understand the characters. It is, however, disappointing that after hinting at character growth for so long, we get slapped back to the beginning again and it seems there is no progress made. There is also a weird sense of revolution/duty in it all. Read some user comment that by the end, it wasn't a couple we were looking at but at a trio of Revolutionary comrades. In some ways though, after a decade of xianxias advocating for individualist/narcissist love, it seems appropriate to pull back a bit to focus on the Asian values of duty. And in that sense, this is very much a Chinese story. Chinese values of filial piety, duty, respect for authority, sadness over fate and karma, etc, permeate. There were glimmers of hope by the third act that progress was made through character growth towards reconciliation of these traditional values with the modern individualist sense of the world - but then the ending sort of smashed it all and shoved us back to the beginning, almost literally. No progress thru rebirth.

Acting:
This is definitely the strongest part of this drama and an important part of its popularity- Both actors seem perfect for xianxias and at a high point in their career. Yangzi being generally acknowledged as one of the most skilled actresses currently is at her usual top game in a familiar role. ChengYi, less popular and perhaps underrated, is a true gem combo of facial expressivity and body agility for all the action drama scenes xianxias require. I hope this work further cements his career and can bring it to new heights. In general, there is no sense that our leads are making new breakthroughs in their artistry- but there is enough sincerity in terms of delivering their best which, as it turns out, is as good as it gets. It is nice to see skill triumph over raw looks, and a wonder to me that despite 59 long episodes of often draggy scenes and lazy directing (it takes two episodes each time for them to die!)- I still can't get enough of seeing the two leads on screen and interacting.!
Whether it is witnessing their happiness or (most of the time) their pain - especially their pain such that one can't help feeling a bit guilty- these two made the whole process addictive.

Music:
Nice music - they put it on sooo many times it's a wonder I didn't get sick of it. So must be really good!

Rewatch Value:
Definitely. There is almost a certain amount of repetition to any story told - this is inevitable as all follow a certain arc. As such, after having watched enough of them, they all feel a bit familiar. However, I still enjoy watching shows for the charisma of the actors, the script's fun dialogue, the beauty of the sceneries. And in that sense, although IS doesn't reach new heights, it combines high quality/talent in all its team that it is just relaxing and nice to watch at the end of the day to lose myself in its fantasy. As good as any Xianxias produced.

Overall:
The last time I wrote a review was for Ashes of Love also with Yangzi and Zhang yuan Ang as scriptwriter. And although the values this production tries to convey is a bit different, it has enough controversy to it that somehow feels worth writing about. Compared to AoL, I'd say that ChengYi is the better (and more mature) actor which makes this production even more pleasurable. The storyline is controversial but perhaps that's a good thing - it isn't quite merely a summary of all the past xianxia stories though as it does try to move towards a better reconciliation of the individual and traditional values/society/duty. I wish it succeeded more at it.
Unlike the other summer fantasy hit LBFD where from what I read, there is a certain mix of Chinese/Western - this is a very Asian/Chinese aesthetic and Asian/Chinese story, I'd say. People would call it "tu" 土 from the set/costumes to the main actor. But the whole makes it somehow more authentically Chinese and interesting in that sense. I haven't yet watched LBFD so not sure if it is a better reconciliation of the clash of cultures in the current world but IS has certainly been a fascinating and pleasurable journey.