And the basic point of the plot turns out to be the aliens' concerns about the Earth people extracting their minerals. If this were a Jon Pertwee story, we would know just what it was all about. But instead we have numerous episodes of peculiar personality-based bickering amongst the aliens, which would be OK if we actually liked or sympathised with any of them, but we don't.
There are some redeeming features. I actually liked the fleshing out of Susan's character and her relationship with the Doctor; shame that this wasn't taken much further in her three remaining stories. I thought that John, the human who is deranged and then cured, was good too but it was difficult to understand what he saw in Carol. And the actual plot that develops in the last episode, that there are insane astronauts hiding under the city contaminating the water supply, certainly does grab your attention.
But as for the Sensorites themselves? Poison the lot and take their molybdenum, I say.