Planet of Evil

The Doctor: Here on Zeta Minor is the boundary between existence as you know it and the other universe which you just don't understand. From the beginning of time it has existed side by side with the known universe. Each is the antithesis of the other. You call it "nothing", a word to cover ignorance. And centuries ago scientists invented another word for it. "Antimatter", they called it. And you, by coming here, have crossed the boundary into that other universe to plunder it. Dangerous.

Terror of the Zygons

Terror of the Zygons is one of those serials that has a reputation. There are a few of these, the stories that are generally considered classics (or the opposite). Usually, even if the story is flawed, it's clear what makes it great.

But Zygons' popularity seems somewhat inexplicable to me. It's a fun yarn, but the idea that it's one of the all-time-greats of Who - particularly in a season including Pyramids, Morbius, and Seeds of Doom is strange.

Pyramids of Mars

"Something's going on, something very contrary to the laws of the Universe.  I must find out what..."

The Wedding of River Song

All of time and space - everything that ever was and ever will be.  At the same time.

The Wedding of River Song finishes Doctor Who's 32nd season by answering many (if not all) of the lingering questions left by this and the previous season, while opening entirely new plotlines.  It's yet another of Moffat's staggeringly complex serial, and one substantially more difficult than Impossible Astronaut because it answers questions rather than asking them, and has to do so satisfyingly.  And, for the most part, it does this.  But that's not what makes it special.