I began this drama with no expectations and no awareness of the hype around it, but having read the manhua before. I think these factors influenced my enjoyment of it.

Rather than just listing likes/dislikes in my review, I thought I'd write about different aspects and what worked or didn't work with them.

Visuals:
Firstly, this is a very aesthetically pleasing drama. Some of the visual effects are breathtaking, especially if watched on a large screen. Costumes were beautiful, and so was the cast.

Acting:
The primary characters have been acted the way they were depicted in the manhua/donghua.
I've seen a lot of criticism about the FL's emotionless face, but that is very true to the source. There's a reason behind the character's lack of emotions, which probably should have been introduced much earlier in the storyline because viewers would have empathized more. She looks and acts like a leader with a lot of responsibilities and centuries worth of grief in a way that I don't think a younger actor could have pulled off.
The ML is supposed to be a hyper, over-enthusiastic young man (actually, *boy* in the manhua), and that's how he has been acted.
Whether it was a good idea to stay so true to the source is a different matter. It's fine when you've read it as I had, but viewers who haven't read or watched the source material may find her stoicism and/or his flamboyance difficult to understand. But this is not a fault of the actors.

Romance:
Don't expect a sizzling romance from the main CP. It's not supposed to be that way. It's about two people who make huge sacrifices to protect each other and the six realms. There are still sweet moments though. You have to look out for micro-expressions to gauge her feelings, while he wears his heart on his sleeve. I'm all about micro-expressions in stoic characters, so I could get her feelings most of the time. She does become more expressive towards the end, and maybe most viewers would have preferred if that change had come sooner and lasted longer.
Regarding the other CPs: Apart from the finale, the interim endings for the CPs follow the direction of the manhua as well. The drama has deviated hugely for their ultimate ending, which could be for various reasons. I didn't mind hugely.

For manhua/donghua fans:
Some key scenes from the donghua have been recreated here, and done really well. There have been some changes, but they were necessary (for example, ML's age).

Editing:
This is one of the biggest problems I (and many others) had with the drama. I've never watched a drama with such poor editing before this. Scenes change before you have time to grasp what's going on, and sometimes they just abruptly cut off. This doesn't allow viewers to emotionally connect with the characters or what's happening. There are frequent long shots of the scenery, which is ok once or twice, but we don't need it all the time. We can admire the scenery as things happen between the characters.

Storyline and direction:
The overall story would have been fine, if only it had been handled well. Instead, there was a slow start, too many pointless battles with the same villains over and over again, too many side characters, and a very irritating and poorly handled storyline in the middle. Important plot points (such as the reason for the FL's lack of emotions) should have been introduced during the setup episodes, not midway through. These factors, along with the bad editing, were probably reason enough for many people to stop watching.

Overall verdict:
My overall review score is probably on the generous side, but it's because, despite finding many faults with this drama, I still enjoyed watching it. I wasn't expecting something deep and meaningful. I wanted a casual watch where my brain could switch off and I could be entertained, and I got exactly that. (Actually, some fellow MDL-ers and I went back and forth with multiple theories, so maybe my brain didn't switch off, but I don't mind.)
I will probably rewatch the whole thing again after a break. I'm hoping iQIYI will have the grace to have it re-edited in the interim.