...the twists are always slightly less good than the episodes themselves I'm finding.
The last one (which was essentially just an extended version of the trial scene in The Witchsmeller Pursuivant from the first series of Blackadder) had a tremendously good cast and a great dark undertone - not to mention DAVID WARNER who is the god of all space. However the final twist was just the first thing you thought of really.
I still think they're yet to match the giddying heights of the utterly extraordinary silent episode in Series 1 but the twist problem is just shallow nitpickery frankly as each episode is a real treat, rammed with interesting characters and excellent guest stars.