Is "The Exorcist III" good?

I remember when I was a kid "The Exorcist III" seemed to be considered a bad movie. I distinctly remember being told that there was only one good "Exorcist" movie. My mother said that she saw it in the theater with my grandmother when it came out and she specifically remembers her walking out complaining about how stupid it was.

Nowadays it's status seems to have risen considerably. I know some people who swear that it's a masterpiece on par, if not better than the first. That's a pretty bold claim considering "The Exorcist" is one of the greatest movies ever made.

What's so good about it? I've heard it described as "atmospheric" and "existential". Is there any truth to this? Or do you think it's overhyped? I haven't seen it yet. Is it necessary to watch the second one?