Drama, mystery, action, fantasy...this series had it all. On top of all that, it had another great quality; it was educational.
It seems to me as if a ton of research went into the show. And not just getting dates right, but other things such as period costumes, decor and vehicles. At times, stock footage was included to spice things up, but overall, the series had what looked like a fairly big budget for the time. The time tunnel itself was impressive in size and the show had a grand feel to it overall, as if it were a lavish play.
The episodes were all based on the fact that Tony and Doug, the two scientists trapped in time, could show up anywhere in any time period. Of course, the episodes [conveniently] almost always took place in famous locales or times in history. Some examples are the battle of Jericho (where they met Joshua and became the two spies that Rahab hid), WWII-era Pearl Harbor (where Tony met himself as a young boy) and the penal colony Devil's Island (a favorite of mine which was accurate right down to having French actors play the parts of the prisoners). In having them land in such places (land being a literal term, as the tunnel seemed to rip a hole in the sky and spit them out), not only was it fun to watch, but viewers also learned something about the period and the figures involved. It was interesting seeming them land in a place for the first time and have to figure out where they were and when it was. There were fluff episodes, too, involving aliens and such, but the series is definitely remembered for the historical accuracy more than the fantasy.
For the fact that it was fun and that I actually learned something from it, I really loved this show. I only hope today's generation gets to see it and come to appreciate it as the entertaining learning tool it was.