The BBC has one major advantage over the majority of channels its not a private company, theres not as much risk involved in making a flop, and because of this they are adventurous, they make shows any American (or other) channel would regard as too risky, and some really hit the mark.
Another thing worth mentioning is the lack of adverts, a full episode of time commanders could be over an hour on some channels!!
If i remember rightly they changed the format and shortened the show half way through the series.

Another show worth tuning into is Battlefield britain, not as in depth as many would like but i think its the right direction for history programs, once you get an interest going, people will go to an effort (such as reading, yes, reading!!) to learn history, but you need something flashy to get them started!
Its on fridays at 9, one of the BBCs, dont know which