Ted strays into some dark territory, exploring the feelings of alienation and betrayal experienced by many children whose divorced parents start dating someone new. Or, as Buffy more succinctly puts it: "Seeing my mother Frenching a guy is definitely a ticket to Therapyland!"
Buffy's dislike and distrust of Ted runs counter to her friends' experience of him, which effectively isolates her from them, too. It's hardly surprising that she runs straight to Angel when she needs a sympathetic ear.
There are plenty of sly hints about Ted's true identity in Greenwalt and Whedon's fully-developed script. It's an uncomplicated mystery story - albeit one with the usual Buffy slant - packed with events that conjure interesting emotional responses from the main characters.
As well as Buffy struggling to come to terms with her mother's new partner and her role as "the dutiful daughter", we have Giles rebuilding his fragile relationship with Jenny following her possession in The Dark Age.
Ted's apparent death is an excellent plot twist, and for a while it seems that Buffy's judgement is highly questionable. Joyce's reaction, and the subsequent police investigation, which raises some serious real-world issues about domestic abuse, both provide rich dramatic potential that the writers are able to casually discard without detriment to their robust story.