First of all you have to realise that this series was produced in the 70's on a limited budget at a time when modern special effects such as CGI were not available. But what has made the Tomorrow People deservedly popular is that the plots and some of the acting were good enough to shine through those limitations.
Pros: 1. Author Roger Price who also got involved with some of the direction was a superb storyteller 2. Most of the young leads are pretty good including the serious John who nevertheless has a dry wit. Other highlights are the charming Elizabeth and Philip Gilbert, the voice of their computer TIM. Peter-Vaughn Clark as Stephen, while not the most accomplished actor, puts in some cheeky performances which provide light moments among the twisting plots 3. Frequent cliffhangers designed to get viewers to tune into the next episode means the action often has you on the edge of your seat.
Cons: 1. Some of later episodes started to lose their way in terms of plot content and cast changes which contributed the eventual termination of the show in 1979. Also some of the attempts at slapstick comedy in the series fall a little flat in the context of the show 2. Some acting is lamentable especially Kenny and the excitable whiny Carol in the early series 3. Don't watch the show for the special effects.
Having said that, the pros far outweigh the cons. What really made this show explode into a masterpiece was the chemistry between John, Elizabeth, and Stephen. It's generally acknowledged that the episodes with this trio were among the finest. I can recommend such stories as the Blue and the Green and Secret Weapon. These can hold their own against the very best of Star Trek or Dr Who, and this great value compilation is worth getting for those episodes alone. PM