I was prepared for a tedious dragging ten-part story with a deus ex machina ending. In fact, it is very good. It looks good for a start, with the various settings and scenery convincingly used. Troughton (especially) and Padbury and Hines really shine, and the guest actors all seemed pretty good to me. (The only one I didn't much care for was the stereotyped Mexican guerilla leader.) The music is not too bad either.
The story is excellent. The first episode gives only the mildest hint of what is to come (British WWI general with hypnotic abilities and a TV screen in his office, soldiers not sure how long they have been where they are) and we gradually build up through a hierarchy of villains - General Smythe, the Security Chief, the War Chief, the War Lord - to the appearance of the Time Lords themselves in episode 10.
The final episode is particularly good, with the War Lord's minions trying to bust him out of the Time Lords' custody, and Jamie and Zoe then trying the same with the Doctor; though he knows, as we do, that he cannot escape. The Doctor's trial echoes his court-martial by General Smythe in the first episode. And the ending, as the Second Doctor spins off into the void forever, must be one of the saddest in the programme's history.