This one puts you in an odd position. It's difficult to argue persuasively for keeping the original Dr. Smith, who has lied to, betrayed, and endangered the lives of the Robinson family on any number of occasions, and sacrificing the replica Dr. Smith (not a robot, but a flesh and blood being, it should be remembered), who proves himself to be a trustworthy, valuable, and productive member of the crew. Even the alien isn't all that much of a bad guy, not wanting to abduct for sacrificial purposes a useful member of the party, but instead through guile selecting the one person who is more of a hindrance and liability to the castaways. I liked the performance of the actor playing the alien, too; he reminded me of the British comedian Peter Serafinowicz. But still, we all know what will happen, and why it must happen. I really am liking these b&w episodes on a cinematographic level, all those moody shadows really help ratchet up the tension and suspense. And Dr. Smith (the true, cowardly one) even gets some action here, liberating himself from the alien's ship. I didn't think he had it in him.