Dr. Who was a long-running show with several different actors playing the lead role over the years (for which there is a perfectly good sci-fi explanation). Ask different generations who was the best "Doctor" and you'll get a rough idea of their ages.
It was made on a very low budget (by American standards), but has attained something of a cult following, even in America. It's hard to describe this to someone who's not been outside the U.S., but the show certainly exudes a very British atmosphere in its humor, etc.
Here's a summary (go to the Brief Introduction for Beginners link):
A Brief History of Time (Travel): Introduction Blakes 7 was a much shorter lived series, but it's another show which has attained an almost cult following. The show has much, much darker undertones than you'll find in Star Trek, and was based around a mottley crew of outlaws on the run from an evil federation
What is Blakes 7 ? I found this comparison while searching, which is pretty accurate:
Star Trek v. Blakes 7 And finally, one of my favorites of the 1970s, Space 1999. Although British produced, it had many American actors, including Martin Landau and Barbara Bain (ex Mission Impossible) and Barry Morse (by which time he'd finished trying to hunt down Richard Kimble to take back to Indiana! <G> ):
SPACE: 1999