It's a really good show, but, unfortunately, the tragedy of it is that while the show researches and presents the evidence very well, they completely misinterpret and misapply it my mind. These are not aliens and never have been. They are angels and demons (and in large part most of them are demons or fallen angels actually, as they are the ones who came to earth and mated with the daughters of Eve, who wanted to be worshiped, etc...but, they do involve angels, too). And the evidence falls perfectly in line with accounts from the Bible (which the show misrepresents often). The show would have you believe that it's the reverse. They would have you believe that biblical accounts of angels and demons are actually aliens and that the Bible got its stories from the extra terrestrial from other planets. They get so close to hitting the truth and just miss it unfortunately. The producers and researchers would rather have you believe in aliens from far off planets than just believing in the truth of what God's word says about all of these beings.
Anyway, it's still a very interesting show and very well done otherwise.