Any way, I want to give it 4.5 /5, but since there isn't that option I voted for 4. I thought this was much better than Planet of the Dead.
A few random musings
1) I guess its classic who in the sense that the Doctor queries that he can't change history. However the story struck me as more of a sci fi thriller, in the same vein as those sci fi where the people get infected / go mad types stories, eg Event Horizon.
2) I loved the bit when the Doctor speaks in the Martian dialect. Don't know why, but it just sounded cool and had elements of classic Who, where the Doctor shows off his alien knowledge only to have the humans say, don't be ridiculous.
3) Time Lord Victorious. Has a nice ring to it. Like NL I would have prefered to see more of this. I do like the Doctor's changing view that he is more than just a survivor. Before he would look on the Time War as a defeat, although the military mind would most probably called it a draw, see "The Armageddon Factor".
Looking at it further, the Daleks came back only to be defeated again. The remainder are imprisoned in the void while the Last Time Lord(s) lives and can go where he pleases. Its a pyrric victory, and the fact the Doctor looks at it that way speaks of newfound optimism and from a character point of view might get rid of some of the emo vibe we have been getting.
4) Adelaide dying at the end, to show the Doctor that he can't change everything, although he managed to save the little people. This was good from a dramatic point of view. Especially tragic as I interpreted things as "well we don't know it really would have worked out" if she still stayed alive. Its indicated that the Laws of time (obviously TL law rather than laws of physics) are derived from theory (although a hypothesis would be the better word), ie that some points are "fixed". Since the TL would most probably never have tested this hypothesis, we don't know whether Adelaide's granddaughter will still pioneer future space missions.
5) I am going to disagree with some people and say that I enjoyed how the Doctor changed things. Its different instead of the Doctor being constrained by plot to not interfere. Sometimes the tropes and cliches just being turned on their head is enjoyable just because its different.
On another note, its hinted the Ice Warriors managed to seal up the infection. I wondered how they did it. The "Flood" seems like a tough foe, although not as resilient as the nucleus of the swarm (The Invisible Enemy). Perhaps they were ruthless enough to simply kill infected members of their race.
