I don't think the "science" is at all important. It doesn't matter that any of it is implausible, that's not what makes it good or bad. The story is everything.
For me, what makes good sci-fi is using that framework to explore the human condition or address moral dilemmas, stuff like that. In this case, facing up to mortality and whether or not you'd choose to sacrifice 36 years of experience to regain your youth.
OK, so having just a 40-minute single episode to work with, you're not going to get much chance to explore that theme in great depth, plus you have to also cram in a bit of being chased by scary robots, but I thought the episode was up there with the likes of The Girl In The Fireplace.
YMMV. I guess it depends what you're looking for.
d.