Of course, if you have seen stuff from Season One, it might feel a bit odd to think of it that way. Certainly, fans of the New Series might wonder how The Reign of Terror (1.8) could be a "season finale" if it doesn't have an army of CGI Daleks in it. Fans of Buffy or Babylon 5 might look in vain for an over-arching plot, theme, or monster. And fans of Lost or Battlestar Galactica will might be puzzled by the lack of cliffhanger revelations in the final episode to get everyone excited about Season 2. It just goes to show how different TV is now. Each episode of Doctor Who was made in a week, and one was made every week, so what is in retrospect seen as a break between seasons was in fact just a well-earned rest for the cast and crew over the summer. The production team and viewers thought in story arcs (the serials) between 2 and 7 episodes long, and it won't be until Season Five that we start seeing any evidence of thought into how those story arcs might fit together. About Time says that, from a production perspective, An Unearthly Child (1.1) through The Dalek Invasion of Earth (2.2) could be considered one season, and The Rescue (2.3) though "Mission to the Unknown" (3.2) another. This actually resembles a little more a "season" as we've come to understand it. That way "Season One" ends with the return of the series' first and most popular monsters, and the departure of the "Unearthly Child" who got Ian and Barbara mixed up in this business in the first place.
