Among all the BL out there this series is indubitaby one of the best, both for the writing, the acting and the directing. The chemistry among the cast members is top notch and the story very interesting even outside the romance part of it.
As for the 2 couples they are equally lovable, the main one is wonderful and the evolution of their relationship is so good to watch. Shaofei with is perseverance and kindness manages to melt Tang Yi walls and defences and it's wonderfull to watch.
The second couple is just plain adorable Zhao Li An is so endearing and sweet that Jack is ensnared by him almost without realizing,
watch it it:
you love angsty stories with perfect ending
if you are looking for a enemys to lover romance
if you are simply looking for a good story with good acting and a bunch of very interesting characters

don't watch it:
well if you do not like mm relationship (but why should you be here then?) or if you really do not like crime stories or if you are looking for cruel vicious gangster and hero police forces.