This has the same kind of structure that you would find in a typical but first-rate 100-episode drama. Predictable story lines, good cast, great characters. And it does it in 20 episodes, which means no meaningless repeats, less padding, no wishing they would all die and get it over with.
The big draw for me was the character development. I loved the various personalities, all believable and acted excellently. There were no chaebols, no one screamingly evil (well, the mother was a real loser), just the kind of people you might have as neighbors. There are really no surprises, plot-wise, but in a season of really unengaging dramas, I appreciated this understated set of performances by a great cast. If you get involved with the people who inhabit dramas, you might enjoy this. I did.