Not much I can say. It's a Sci-Fi-gasm. Given my own love of the genre, I can't help but enjoy the nuance in this that would be missed by any other than a Sci-Fi fan.
Having said that, I don't know how much appeal this could hold for someone who was not a devotee of the genre. Without prior knowledge of who Moffat is, an understanding of the Doctor Who universe and the way he has managed to reinvent the series by basically ignoring most of the previous series, a substantial amount of the humour would be lost.
(Am I the only one who sees a remarkable similarity between the cracks in the universe and the Red Dwarf crew being destroyed by their future selves?)
So, ignoring my own side note, I have had to keep the score down here as it is a limited concept with limited appeal