2. The Waters Of Mars (Tenth Doctor)
This is one of my all-time favourite episodes. The dark side of the Tenth Doctor and the believable, multi-national team of Bowie Base One. The older lady companion with no sexual interest in the Doctor and the well-crafted background and the fall of Earth which lead to them to traveling to Mars in the first place. The world the Tenth Doctor steps into on his second-last adventure feels three dimensional and believable (as opposed to some adventures which do feel a little contrived) and should be seen by more people. It barely needs changing, just expansion. We could all use another ten to fifteen minutes of the Time Lord Victorious and perhaps some heavier foreshadowing of the following adventure and the return of the Time Lords and the Master. I can but dream.