The first and the best episode in my humble view; I prefer the 139 minute version (the premiere broadcast). This sets up the characters, situations and the BG universe generally very well.
However, it is a tad pear-shaped in that the resolution is rather stupid: Carillon made of tylium, which catches fire from laser battles and explodes. One of the main problems with all of classic BG is the appalling science and occasional bad plotting. The series was made by people who only had the idea of adapting old war, espionage or western plots rather than come up with mindblowing scfi concepts (ala Star Trek or Babylon 5). It's made in the grand tradition of adventure fiction and pulp space opera and as such is rather wonderful.
The one genuine scifi conceit is the Von Daniken ideas espoused, and these are good ones in my view. However, it's fair to say that between 1968 (when Von Daniken published his book Chariots of the Gods) and 1978 the conept was well-used in scifi TV; ie Doctor Who: The Daemons (1971) and Image of the Fendahl (1977); Nigel Kneale in his Quatermass and the Pit (1958-59) had all been forerunners.
BG was also not held in high regard in the scifi community with top writers Isaac Azimov and Harlan Ellison castigating it ("One of the worst TV shows ever"). Nor was it held in high regard by the critical fraternity who merely saw it as cashing in on Star Wars despite BG starting it's road to production in the late '60s as Glen Larson's Adam's Arc concept.
However, to my mind BG was an historically significant show in US TV terms: It was the first attempt by a weekly adventure series to have an ongoing story arc with episodes having to be screened in a very specific running order. This has become the norm now, but was groundbreaking for US TV at the time.
I was living in Rochester New York back in September '78 and was allowed to watch the first hour of the premiere only as in those days we only had one TV and my parents watched Masterpiece Theater over on PBS (WXXI Channel 21 Rochester NY). I had to make do with the novel, the Photostory and the Marvel Super Special until the 1979 release of the 124 minute theatrical cut which I saw at the cinema.
Compared to other BG episodes I'd rate Saga of a Star World:
out of five.