1000 Misspent Hours says, "it accomplishes much more through subtlety than its budget would ever have allowed had its creators aimed for spectacle instead." Moria says, "The film has a great opening. ... Alas, once we see the robots -about 30 minutes into the film– Target Earth takes a nosedive."
Weird Wild Realm likes the robot and says,
And even though the robot appears to have been constructed from large biscuit-tins; flexi-ducts then spray-painted silver, it's even so a wonderful piece of art deco minimalism, inspiring many a child of the 1950s to build their own robot costume from cardboard boxes. ... Well acted, cool robots, with a more than adequate array of B-actors headed up by Richard Denning, & told with poker-faced conviction. Truly worthwhile.TCM has information. Rotten Tomatoes has an audience score of 27%.