MDL be like:

-Get a drama with dumb writing, black and white characters, overpowered gary stu protag who has titanium plot armor, and an ending where all bad guys are punished regardless of their crimes and ml and fl live happy ever after: FUCKING MASTERPIECE SLAY GIRL!!!!!11

-Get a drama with clever writing, multidimensional characters, where protagonist struggles all the time to get what they want, and the ending is unhappy or bittersweet: REEEEEEEeeeeee *hellish screeching*

It so happens that Big Mouth (should be Big Mouse) is in this second category, and this explains any complaint or bad review you might have read of it. Really it's just MDL idiocy, the drama is great.

The only faults I could find are:
-The last episode felt rushed
-The ML can't act and was clearly chosen just for his looks. But it actually works in his favor here, somewhat, considering what kinda character he plays.

Extra credit to all the humorous and unintentionally humorous scenes that you might not expect from this kind of story and to acting of Yang Kyung Won who just dominated every scene he appeared in.