Time Tunnel and Voyage, started off good but turned into "monster of the week" shows.
To be fair, Time tunnel was not a monster of the week show. They had no monsters whatsoever, but they did get into space aliens and futuristic societies that didn't come off very well. The series got pedestrian. Voyage did embrace monsters, but did so from the very beginning. They just because more frequent and repetitive. I like monsters, so I had little problem with this.