This series was an excellent review of most of history's UFO stories, some very well known, and others less so. The only issue I have is with some of the names of the episodes, like "Britain's Roswell". This episode deserves it's own name, like "The Rendlesham Forest Incident". This and several other episodes, seen with an open mind, will have you questioning whether we really are alone.
I encourage everyone to watch any one of the series and then do some serious research into the subject. Don't listen to the BS that most people spout about UFOs and aliens. Go and check out the Disclosure Project and watch and listen to hundreds of credible servicemen and women tell their stories.