Unlike the more recent way of re-introducing old monsters, IE introduce a lot of them in a bloated two-parter filled with weird design choices, companions weeping and scripts that just baffle logic such as Rise of the Cybermen/The Age of Steel, The Sontaran Stratagem/The Poison Sky, and The Hungry Earth/Cold Blood, this returns to the Dalek way of doing it; faithfully reintroduce one of them, a frightening, ruthless representation of its entire race, and have them trapped in a closed, confined area.
Would've been a 9 if not for the complete tonal misjudge at the end where we get happy, triumphant music and characters acting like it was the end of The Empty Child/The Doctor Dances just because he spared their lives, even though he, uh, murdered half the crew and they only barely survived through nuclear annihilation. But no, he decided not to be a Harriet Jones, so let's get Murray Gold doing his "Hooray!" music and have the characters grin and laugh like buffoons.
Other than that, this was a tense, tight, Troughton-era base-under-siege homage that felt claustrophobic, had great character moments for Clara's second time out (compare this to how Gatiss wrote for Amy's second time out!) as well as for the supporting characters (
David Warner). Not the most original Who story ever, not a classic, but compared to other New Who trying to do similar things, it was very well-executed and damn enjoyable.