First i would like to say that i understand why people don't like this series, but i am here to give the pros and cons of it all.
Plot: The story is rather good, but it's execution was a bit awkward at some parts and i easily skipped through the product placement bits cause it added nothing to the story itself. I also skipped a duo's parts cause, again, it added nothing much to the main plot.

Characters: The characters are not bad, but it lacked a bit more of construction specially on Kamol's hardcore bed preferences that were able to chase away any and everyone. Kim is also a character that had a nice base for it's character but ended up falling into the worst (my opinion) kind of BL cliché near the end.
Also, the character of Cherry is the biggest BL cliché of all. Ging Areeya (Cherry), who was great and sweet in "My ride", made me feel like they just tossed her here to add to the drama and with no base for her character at all, besides the fact that she is obsessive, annoying and incredibly beautiful. (Last one is my opinion)

Music: Oh, the music. This one was the worst of the worst. For all "tense" or "mafia" like scenes there was this ONE song that repeated again and again. Same goes for the main "romantic" song of this series. I heard it so many times that it felt like they were trying to brainwash me with it.

In the end, Unforgotten night is pretty enjoyable for a one time only watch and easily forgotten in the big sea of many other good dramas from the BL genre. I just gave this one a 6 point overall cause that 7 i already consider it to be the average for many of the dramas i watch.