I generally stick to the 4-episode rule before deciding to drop or not. Before I watch any drama, I do research. Tons of research (rip). I look into the writer-nim and PD-nim, cast, plot, etc etc. Some dramas start off okay, but then go downhill. A few other dramas start of slowly, then pick up. For example, I was okay with the first four eps of Bride of the Water God, but it got reallllly boring after that, so I dropped it (I tried to stay for NJH but couldn't). I had to try Reply 1988 three times before getting into it (currently #2 in my top 10). I rarely drop after the first episode, but when I do, it's on the dramas that feel messy from the start or because the characters are terrible. hope this helps :-)