Revealing mistake: The fake snow in episodes one and two is effective - with the exception of when the Doctor is digging up the second Krynoid pod, where it is painfully obvious the snow is styrofoam packing peanuts.
Plot hole: At the very end, the TARDIS materializes in Antarctica and Sarah comments that they've returned. But the TARDIS was never there - the Doctor and Sarah went to Antarctica by helicopter.
Suggested correction: But THEY were there.