Its professional and is as trustworthy as TV shows get. Personally it Space, Science and history based documentaries are always the best, whilst those which examine recent fads in the media, such as Atkins or ADHD are normally dull.
They never fail to explain well what thier talking about, and without looosing its professional approch they also manage to tell it interestingly.
Horizon over the years has opened my eyes to many things I wated to know about as well as things I was glad to have found out about. Its nice to know this show is still around after all these years. Its good to know thier are trust worthy educational shows around. I watch enough junk as it is!