Wow, it's amazing how many didn't like this movie. I've read everything Whitley Streiber has written, and have loved it all, even when it wasn't so great, which were really few and far between. But think about it: if you went through what he and his family -- and especially HE -- have gone through, you might be a little ... compromised too.
Still, in my opinion, even though this movie seemed a bit tongue in cheek and irreverent in places, I think it may have been just Whitley's way of trying to 'put on a brave face,' especially for his son. I've been receiving Whitley's newsletters and listened to his podcasts on his Unknown Country site for years where he talks about these experiences and others who have also experienced them have talked about them. If you don't believe, fine. Whitley, Anne and Andrew (and their friends) believe this happened to them. Who's to say it didn't? Just keep in mind that there are a lot of us out here that have gone through similar experiences to Whitleys.
As for the writing, he did the screenplay. I think he might have been just playing around with a new (for him) medium.