This one is a real gem of a time travel romance. Ironically, I actually found the world-building and time travel aspects more interesting than the romance at times, but I'm going to put that down to personal taste.
The production quality for this show is truly excellent, the cinematography, music, and editing are all absolutely wonderful and serve to create that romantic and melancholy atmosphere that seems to have resonated with so many viewers, myself included.
The performances and script are absolutely stellar as well; you can tell just how much love and effort was put into this entire story.
The characters are all interesting and complex and their sheer likeability makes all aspects of the story more enjoyable and impactful, from the romance, to the humour, to the tragedy and drama.
Personal favourites of mine are James and Mei, but I honestly would happily watch an entire drama dedicated to pretty much any one of the supporting characters.

A lot of folks have praised the show for the varied and diverse relationships it depicts, as well as for how unflinching and brutally honest it is in showcasing the realities of life for servants, the lower classes, women, and queer people in 1920s Thailand - and rightfully so! The show-runners do a fantastic job of highlighting the social and systemic oppression these marginalised groups used to and still do face to this day in a way that is both realistic and relevant to story.
However, there is one aspect of these depictions that I take some issue with, which is the sheer amount of rape scenes included in the show. Don't get me wrong, they are very well done and brutally effective in how uncomfortable they are to watch, but some of them felt unneeded and borderline gratuitous. I don't think any of them are intended to be outright voyeuristic or titillating, but some of them end up unfortunately somewhat coming off as such, at least in my opinion.
If nothing else, I feel it's necessary to give potential viewers a heads up about this, so consider this your trigger warning.

All in all though, I really loved this show and can't wait for a potential season 2 to pick up where the finale left off (and shout-out to the kind souls in the comments who explained the ending more thoroughly than the show did). Seeing all the character dynamics change and evolve in a present-day setting would be an absolute delight and I hope we get to see it.
Meanwhile though, I would recommend this show to anyone looking for a beautifully shot, beautifully realised historical romance, or to any enjoyers of serious, yet wonderfully charming queer love stories that feel almost time-less.