This is a hard one to watch in one sitting. It is best to watch no more than one episode a day, and I think you will find it very enjoyable. This is the first story to feature the Time Lords, and the first time we learn that the Doctor's people are not from Earth. The story kind of drags until Time Lords show up.
I quite enjoyed this adventure. It was originally to be a 4 or 6 part serial, but another script fell through and it had to be padded to 10 (!) episodes. The leads to a few episodes where a great deal happens, but the characters end exactly where they were at the start of the episode. Early, cheap, but still entertaining. And Troughton is excellent. So few 2nd Doctor episodes survive, I find it hard to judge compared to others.
Reasons to watch : 1) First use of a Time Lord Message Box. 2) More SIDRATs than you can shake a sonic screwdriver at 3) The Time Lords!! 4) Regeneration to the 3rd Doctor.
SPOILER ALERT!!! The Doctor and his companions arrive in a WWI war torn landscape on Earth and are captured. The Doctor is sentenced to death by the leader of his captors. After his escape the Doctor learns that the war is really an experiment run by aliens bent on mind control and galactic domination. He also discovers a collection of interconnected dimensional portals, each running a separate war; Romans, Civil War, Mexican War, etc.. Everyone is a prisoner in this malevolent scheme and the Doctor must stop it. In so doing he notifies the very people from whom he is running; the Time Lords. The Doctor tries, yet fails, to escape the Time Lords and is tried and found guilty of theft and disrupting the Time Lord's way of life. He is forced to regenerate and banished to the planet Earth.