I would personally not classify this as BL but as a drama with gay characters and issues. This doesn't make it better or worse, but the viewer's expectations should be set accordingly.

The most significant aspects of the series are that it deals with the issue of homophobia and rape rather seriously. Given the focus of the story, it would have been better if the series had toned down the sweetness at the beginning: Shin's unabashed admiration for Keng (Episode 1) strongly suggests something more than just idolization, and the revelation that Keng is attracted to Shin (early in Episode 2) even before they bump into each other sets things up for the development of a romantic relationship between them.

The tenderness of Keng towards Shin is shown through his inner thoughts and isn't likely to be feigned (unless its an act of self-delusion). It is thus hard to be convinced that Keng would rape Shin (and violently beat him up) at a slight provocation. We do see a hint of a potentially violent streak when he hits Man for an act of malice, but his outrage was justifiable and he certainly isn't hurting someone he is in love with. The sudden and severe violence Keng inflicts on Shin compromises the overall coherence of the portrayal of Keng. Perhaps there is a point being made about how acts of violence like rape can be inflicted by the people one trusts, but it isn't coming across very well.

The depiction of Keng is complex. After hurting Shin, he appears to be sorry and still professes to love Shin. (I guess this happens with a lot of cases of abuse, so it is reasonable enough to show him doing this.) But he also disappears until after Shin has recovered physically, then he threatens Shin with a clip he has recorded during the rape, keeps pestering Shin and even blames everything on Man after Shin attempts suicide. Such behavior threatens to push the character beyond the boundaries of credulity.

As for Shin, it is not clear whether he ever has romantic affections for Keng. This doesn't matter because he was not willing or ready to start a relationship with Keng, so Keng's behavior is wrong regardless of how Shin might have felt towards him. Nevertheless, I can't quite make sense of why he seems infatuated with Keng but tells Keng that he might like guys some day too when Keng confesses that he is gay. It would have been better to show Shin's admiration for Keng without hinting at romantic interest at the start.

For a series of merely three episodes, The Effect deals with plenty of heavy stuff, but the bulk of the heaviest stuff is confined to about one episode. Perhaps commercial considerations are involved here. It invites us the ask what the cause is for the effect that we see. Shin blames himself before committing suicide. But we can also quite clearly see that Keng's violence is what ruins everything for himself and Shin. Even more seriously, the homophobia in society is perhaps to blame for Keng's denial to Man that he is gay (which triggers Man's indignation and leads him to post a photo of Keng and Shin that causes misunderstandings) and the pressure that judgmental comments on social media put on Shin.

The ending is also unsatisfactory. We don't know if Keng or Shin (if either of them) gets knocked down by a vehicle. The ending is open-ended (which is fine), but it is also totally unnecessary (which is not so fine). The series could simply have ended just a few seconds earlier, with Shin graduating (the happy part) and with him reflecting on how he is left to cope while those who have been cruel with their words have forgotten the events (the sad part because we see that there's no way Shin can totally get over his traumatic experiences).

Perhaps one other concern is that the only overtly gay characters are depicted so negatively. Shin's sexuality is too ambiguous although he is not negatively depicted. There is a hint of something going on between Pramote and Bright (Shin's friends), but it's merely a hint. They could have been used as a nice contrast to Keng and Man, who turn out to be really awful gay men. Bright, though, is truly a bright spark in the series. I look forward to his appearance even though Yacht (the actor) seems to be playing a similar role to his role in Love by Chance as a seemingly frivolous but fiercely loyal and true friend. He single-handedly makes the series more enjoyable.