"He was a person. And I killed him."
It helps that "Ted" is a really strong episode even if we ignore Ritter. The episode is structurally pretty interesting, shifting between two very non-fantasy stories: first, the story of a two-faced, abusive boyfriend who seems normal and likable to everyone else, and then, the interesting dilemma of how Buffy reacts to killing a human being. The latter is slightly undermined by the discovery that Ted was a robot all along, but I think the implications of Buffy actually having killed a person are something that the show couldn't really have dealt with as it was.
I think one of the strengths of the episode is that it needn't have had the science fictional robot concept to work as well as it did. It's sufficient for Ted just to have been a really messed up guy... which of course is Joyce's understanding of the whole thing. And the relationship between Buffy and Joyce is one of the best things about this episode, picking up from their little "moment" in "School Hard."
The episode is fleshed out with a minor B-plot involving Giles and Jenny Calendar, revisiting their relationship for the first time since "The Dark Age" as they try and figure out where they stand, which by the end is a lot better than where they were in the beginning. Their fight with a vampire in the graveyard is nicely juxtaposed with Buffy's second confrontation with Ted. Meanwhile, there's even a C-plot with Xander and Cordelia trying to figure out where they stand. Apparently, they stand in a utility closet making out. Although standing is optional.