Favourite episodes?
My choice would be:
1.Swan Song: Really didn't see the final twist coming until very end.
2.Sleeper: A clever double-twist story with shocking ending! Suitable conclusion to 1st series.
3.Mercy: Another clever double-twist scheme.
4.Motive: We know whodunit but never know why until last. Also I like the character development of husband and wife in this episode.
5.Regrets: It really takes you into the point of view of the killer. Also like the who-in-prison-trick played by the writer.
Other episodes like 'Victim' 'Passion' 'Suicide' 'Vigilante' 'Landlord' are also among my favs. Usually episodes with twists are better than those simply focus on characters.