The film has a great opening. It sets up a classic deserted city scenario with Kathleen Crowley awaking in a hotel room after what appears to be an overdose of sleeping pills, finding there is no power or water, nobody else in the hotel, and then walking out into the deserted city and finding dead bodies littered about, before eventually encountering other survivors. There is an extremely good sense of mystery created in these scenes, in the film leaving us wondering what is going on. [The set-up may well have been inspired by the similar opening in John Wyndhams then recently published The Day of the Triffids (1951)]. The first appearance of the robots, seen only as a giant shadow outlined against the entire wall of a multi-story building, is also effective.
Alas, once we see the robots about 30 minutes into the film Target Earth takes a nosedive. The robot is no more than a man in a clunky suit with accordion arms that shoots a series of poorly double-exposed raybeams. Despite concerning itself with an alien invasion of overwhelming force, the film is so cheap that only one of the robots is ever seen throughout. Moreover, the film also chooses this 30-minute point to cut away to a series of scenes with the military standing around plotting the counterattack. These scenes explain everything that is going on, whereupon all the mystery that has been built up to that point dissipates. Target Earth would have been much more effective, one suspects, if it had kept the robots and invading aliens as merely shadowy figures on the wall, had dropped the military scenes and focused on the mystery about what is going on.
Outside of the military scenes, the rest of the film is taken up with the survivors sitting around in a hotel room. All the alien invasion takes place off-screen and is only relayed through what the characters tell us. There is a competent cast but the dramas involving them are dull moreover, we learn almost nothing about any of them as characters throughout. The eventual attack back is represented by stock footage of bombers, with the day eventually being saved by a last minute techno-babble solution involving a sonic oscillator.
There have been a number of other films with similar titles the UFO film UFO: Target Earth (1974) and the alien conspiracy tv pilot Target Earth (1998) although none of these are related to this film.