In a nutshell:

The story is interesting though some may bemoan the way the series doesn’t seem to have a major conflict or point of tension for quite a few episodes. However, the series never feels slow or boring to me. There is a lot to love about this series because it doesn’t always tell the story in an in-your-face manner. But this could well be its weakness too. For example, if it had emphasized how one of the main characters’ (Pharm) incomplete recollection of his previous life early could pose a problem to their relationship, the tension and suspense built could have maintained the interest of more viewers.

In a coconut shell:

The series starts with the tragic double suicide of Korn/In, certainly not the lighthearted schoolboys-fall-in-love stuff that is so common in BL (though the characters are students). The double suicide is the result of parental objections to their relationship because of their sexual orientation, a rather serious consequence compared to popular BL series that treat the topic of objecting parents less seriously (e.g. Together with Me: The Next Chapter in which the parents change their minds, and Dark Blue Kiss in which the parents are surprisingly open-minded). The seriousness in tone, though not all that persistent, makes it different from a lot of BL that focus on the couples’ relationship without such a strong regard for the society in which the story is set). Where the Dean/Pharm story is concerned, the use of common BL tropes (like a “straight” guy falling in love with another guy) is rather sparing. This may be a good thing, but the side couple (WinTeam) may appeal to BL fans more and may be more conventionally BL.

In the parts of the story that use common BL tropes, the series does become more like BL and somewhat less realistic. The inclusion of a BL fangirl of sorts (Manaow) and the way Dean’s swimming team do not seem to bat an eyelid when their captain brings his boyfriend with him on a team outing are where BL fans find themselves in familiar terrain, though we can guess how often that happens in real life in Thailand. Interestingly, these elements seem to be used to contrast past and present, making a point about how increased openness towards homosexuality in society makes a huge difference for same-sex couples and even the two fathers who live in regret after their sons’ deaths. The society in the Dean/Pharm parts of the story feels much less oppressive that the atmosphere in the Korn/In story. We can see this from the minor characters’ behaviours: whereas Pharm’s friends accept and encourage his relationship with Dean, In’s good friend only quietly feels happy for him when he sees In together with Korn. Such subtle touches make the story rather interesting and worth re-watching.

There doesn’t seem to be a rush to bring the plot to new heights of tension. There is neither an excessive preoccupation with kissing and sex scenes nor an aversion to them. Although a number of viewers seem to find UWMA to be rather slow-moving or that it’s not clear where the story is going, I have a different opinion. In fact, the story is fairly well-paced, with the flashbacks seldom being unnatural as they show the parallels between the previous lives and the present lives. I suppose one thing that frustrates some viewers is the way the Dean/Pharm storyline doesn’t seem to have any obvious conflict for a large part of the series, which may give the impression that it is going nowhere. However, I like the way events are foreshadowed and how the characters slowly recall and come to terms with their past lives. As I watched each episode on a YouTube playlist, I get to the last part before I know it (it’s quite a different experience when it comes to series like I Am Your King Season 2).

Another aspect of the series that I like is how Dean and Pharm have different personalities from their past lives. The differences are more subtle in Dean, who seems calmer but also more determined to make his relationship work out than Korn. As for Pharm, while he’s clearly attracted to and in love with Dean, he does not rush into the relationship. As a really good cook, Pharm is set apart from In who cannot cook to save his life. This difference isn’t merely superficial for the patience and skill with which he cooks indicates a different personality. Both Dean and Pharm seem to have “learnt” something from their previous lives. The dynamics of their relationship are somewhat different too. While we see more passion between Korn and In, we see more tenderness between Dean and Pharm. The interplay between the parallels and differences indirectly creates suspense: will the couple finally have a happy ending, or will history repeat itself? Most of the time, the story seems geared towards a happy ending but there is foreshadowing of a problem to come, especially in a scene where a monk reminds the couple of the importance of forgiveness. In the end, we see that Dean/Pharm must reconcile with the people in their past lives and settle their unfinished business before moving on as themselves in their present lives. It seems paradoxical in the end, but it makes sense: Dean and Pharm have acquired new identities and cannot be living in the shadows of Korn and In forever, so while accepting that they are reincarnations of Korn and In, they must still be able detach themselves from their past lives. (An interesting scene in the last episode with Dean and Pharm dreaming of Korn and In as third parties and not as themselves for once shows that they have finally managed to move on as Dean and Pharm, not reincarnations of Korn and In.)

I also love WinTeam in this series although it often looks like the WinTeam scenes are a teaser/test for a possible Season 2 which will focus on them. I would love to watch a Season 2 with WinTeam as the focus though even with the same production team, I believe a Season 2 with WinTeam will be enjoyable in a rather different way. If this series doesn’t appeal to you, you could still give Season 2 a chance if it is made.

Edit: After considering why I've been feeling that something is a little lacking in this series despite my love for it, I realize that there isn't that much on how the characters fall in love. For Dean and Pharm, each immediately feels like the other is the one on first sight because of their past lives, so we can only look to Korn and In. But while we can see the depth of Korn and In's love, we don't see enough of what makes their love so strong. Our involvement in their story would be stronger if there had been a bit more showing Korn and In's love for each other.