An odd choice of premise given that the real-life Project Blue Book had been closed ten years previously and, if not officially discredited, had certainly faced serious challenges over its motivations and probity. In partial fairness, though, some episodes in the series depict the public accusing the team of a cover-up.
In general the stories are played out terribly slowly - often padded out with ponderous, purposeless shots of characters walking or driving past the camera or exterior shots of a helicopter. In the second season these were supplemented by "banter" scenes between our heroes which lacked any humour and did nothing to further the plot. In each episode scenes of the UFO's arrival are repeated a number of times in order to hit the standard 48-minute runtime. Cut out all the "waffle" and you'd probably trim ten minutes from each episode without losing any of the plot.
The acting from the two leads starts out as rather "stiff" and characterless but they improve slightly over the course of the the first season. Aldine King, as Gatlin's secretary, is awfully underused but much more interesting to watch!
William Jordan (as Gatlin) disappeared after the first season - presumably abducted by aliens. He was replaced by Edward Winter (as Capt Ben Ryan), leading to a more of a "spark" between the two lead characters. The second year saw production improvements such as more modern-sounding incidental music and sound effects and more "dynamic" camerawork.
The visual special effects are quite well realised in some episodes, taking into account the era the show was produced. That said, some camera focusing was poorly directed as it presents no impression of depth-of-field, rendering the use of small models rather obvious. And presumably the FX sucked up most of the budget as many of the visitors' ships in the first season emitted sounds that had been taken straight from 'Star Trek', produced a decade before.
It's difficult to recommend any particular episodes as they are all fairly consistent in plot.
The show is very rarely seen these days (in the UK I gather it was last broadcast by The SciFi Channel in the mid-1990s). But this isn't surprising and it's certainly no "lost classic". Overall this pedestrian work has little more than curiosity value - and did well to last its 26 episodes.