Angst Aversion - a lot of the episodes with Laura's lovers, and the poaching escapade. The dramatic tension, and possible consequences for the poachers if caught, has considerable emotional impact. Robert Timmins' role in protecting Alf and Edmund, and the consequences for his job and home life, also makes the last episode of Season 1 climactic. The cold war between Fisher and Daniel Parrish also makes the finale of Season 3 tense.
Tearjerker: Zillah's death in the final episode of series one
Archie Arless' death from measles in series 3.
Some of the scenes where Laura is having to say goodbye to another young man, and certainly the scene where Fisher's mind is changed by Robert's last minute intervention. Laura is devastated enough to spend the night of the clock inauguration in bed in tears listening to the celebration. Anyone who has been through this knows exactly what she's feeling.
Narm - Gabriel Cochrane. Most of the male leads during the series were just on the right side of sickeningly sentimental. Gabriel introduced a variant of Victorian Novel Disease - the man fallen on hard times trying to make a new life for himself - and singlehandedly pushed the Narm quotient Up to Eleven.
Caroline Arless' displays in court in the first series are pretty much the most embarrassing moment in the entire run. Dawn French introduced too much comedy into the series and upstaged most of the other characters. Once she left, the series got ten times more believeable, partly because it was pretty ridiculous of the writers to use a debtors' prison story thirty years after they were abolished, and partly just because Dawn French can't do straight drama. Her series four appearance is less Narm-ridden though.
Some of Thomas Brown's scenes tended towards the Narmish, though his character was at least appropriate for the age; he appears a bit of a caricature but at least some other religious characters - Miss Ellison and Benedict Marley - are presented more sympathetically. In the book he was a Revivalist, which would have fit him better than his CofE affiliation did in the TV series.