Too much detail on UFO models!!!
All the photographs of supposedly real UFOs almost universally show them as being smooth surfaced and almost featureless. Yet the guys who created the UFO models for this show look like they went crazy with model kits and put an overwhelming amount of stuff hanging all over their ships. Should they not have tried to copy existing photographs?
Also, for the scenes that supposedly happen at night, most people and places were obviously filmed in broad daylight, but the UFO shots are all shown against a black sky. This switching back and forth between blue sky/daylight and black sky really ruined the continuity of the show for me.