Received fan wisdom tells us that this is the worst Who series ever made. Not having seen it since it was first on TV, when I was 7, my memory was a little hazy and I was willing to give it an unbiased view.
On reflection, I am of the opinion that while there is much wrong with this series, such as the Doctor's prickly character, Peri, bad costumes and shakey plot, it's not the worst. The plot is a bit wobbly, but not as incomprehensible as some. Colin is a good actor, and does well with the character given to him, and in some scenes really shines. The central problem, however, is the choice of actors for the twins. Wooden is an understatement. They make Thunderbirds puppets look like Olivier in Richard the Third.
On reflection, 2 stars. Not the worst story, but certainly not the place for newcomers to the series to start.