20. The War Games (Second Doctor)
When the first Doctor regenerated in The Tenth Planet, it was sort of a rushed thing. William Hartnell was getting sicker and couldn't remember his lines, so they realized he had to go, but they didn't want to lose their hit show. So they cobbled together the whole regeneration thing pretty quickly. However, when the actor portraying the second Doctor - Patrick Troughton - decided to leave, they were able to do things much better this time around. Terrance Dicks (then the script editor) and Malcolm Hulke were able to pen an enormous 10-episode epic to give the good Doctor a proper goodbye. When he and his two companions land the TARDIS, they walk out into what appears to be the middle of World War I. They get captured and interrogated under suspicion of being spies. They get a rushed, obviously phony trial, and sent off to be executed. They manage to escape and steal a truck, whereupon they encounter fog. They come through the other side and see.... Romans. An entire Roman army bearing down on them, with chariots and phalanxes surrounding them. I would say more, but I've away far too much already. Suffice it to say, the following story provides more twists and mysteries than you would ever think possible.
19. Remembrance Of The Daleks (Seventh Doctor)
Remembrance of the Daleks was the final appearance of the Daleks in the classic series of Doctor Who, and shows us what Doctor Who would look like were Michael Bay allowed to direct an episode. But in a good way! The seventh Doctor returns to 1963's Earth to pick up a package he had left himself, but learns there is a tiny contingent of Daleks hiding out there. It seems in the aftermath of Revelation of the Daleks, the war between two factions had grown worse, and now an army of Imperial Daleks are on their way to Earth to finish off the rebels. The following four episodes - which it has been suggested was the beginning of The Time War - are a breathtaking montage of action and explosions. So many explosions.