I started watching because this is one of the danmei drama adaptations I've seen being recommended the most. I was also encouraged by the rating here on the MDL page for the drama.

I can say that I understand why I saw it being recommended it so much. For anyone who is a fan of BL or bromance dramas/series, this is gold: the two main characters are great actors and have excellent chemistry with each other. While it doesn't get as shameless as in other dramas I've watched (namely Word of Honor), this show still makes it very easy for me to read between the lines and consider it a full-fledged love story rather than a bromance. Shen Wei would make it very hard for anyone not to fall for him whenever he lets go of his calm and collected attitude to help Zhao Yunlan in any way possible, and the Guardian himself is unable to act all cool and detached for long before starting to care for Shen Wei deeply.

The problem of this drama is just... everything else. The story felt very chaotic and hard to follow from the get-go to me, to the point that I had to stop myself from dropping the drama altogether after the first two episodes. The events of the story are not very appealing, so even when I had to feel worried for the characters or excited to see what would come next, I wasn't able to feel much. Unfortunately the same goes for the cast other than the two protagonists; even the most important secondary roles didn't feel much relevant nor interesting. Even the main villains of the story felt more annoying than actually charming or threatening in any way.
All of this was made worse by a very fragile worldbuilding, with obscure rules for supernatural and sci-fi elements that often made me ask "why isn't this character using their power on this occasion?", "if that character had been able to do that all along, why didn't they do that sooner?" and similar.
The pacing of the story was also off, with elements of the plot and some characters that would have benefited from having more time to better explain their situations, and moments in the story that were made unbearably slow and detailed for no real reason.
If all of this wasn't enough, a huge flaw of this drama was the production, which felt... cheap, for the lack of a better word. I usually don't mind lower budgets at all and I hardly even point it out when I notice it, but this time around it was just too annoying. The CGI and other digital effects made me feel like I was watching an early 2000's movie, most of the props and the costumes looked too fake for me to suspend my disbelief, and often times even the audio quality was bad and distracted me from the story further.
While the acting of the main characters was very good, I can't say the same for the rest of the cast. The best I can say for them is that it was decent most of the time for some of them, but in many instances I felt like the acting was too exaggerated and dramatic, or just very stiff and unnatural, depending on the actor or the scene.

I chose to give Guardian a 7 out of 10 because, despite struggling toward the end, I was able to watch the entire thing, and I actually enjoyed myself when I was focused on Shen Wei and Zhao Yunlan. They're the only reason why I would recommend this drama to anyone: it's a good bromance and the fans of the genre will definitely love it. My only warning is to lower your expectations in terms of plot and setting: if you're looking for a good fantasy/sci-fi drama, you should look elsewhere.