I really liked “Waters of Mars” quite a bit. I personally didn’t mind the darker turn that Tenant’s Doctor took at the end, especially since it didn’t take long at all before he began to see its repercussions. I’m excited to see what the next two episodes bring.

I wonder: did any of you catch the “four-knock” sound effect at the end of the episode? I’m not talking about the three-knocks at the Mars station – I’m talking about later, during the final scene of the episode, back on earth: after the Doctor has his talk with Adelaide and she goes into her flat. As she opens and passes through her doorway, there are four knocking sounds that play on the soundtrack. Almost like drumbeats. I’m sure this was intentional, though I doubt it is the actual “he will knock four times” payoff – I suspect that is yet to come.