1000 Misspent Hours says,
Cool idea, inept execution. The unimaginative directorial style works against the movie at every turn. The script asks a lot of our disbelief-suspenders, and doesn’t give them much to work with. The acting is particularly shabby
we all know why we really watch these movies— we want to see cool rubber-suit monsters. And The Mole People has a veritable army of them. It’s not enough to make it a good film, but it’s enough to make it suitable entertainment for an otherwise unoccupied Saturday afternoon— which, after all, is what it was really designed to be in the first place.
There's a lengthy examination of the characters, plot, etc. here.