Concept: An HP Lovecraftian 'Elder Gods' story of someone being driven insane by seeing the world as it really is.
What's good: The 'something's not quite right' sections are very good, and the samples of other Hobb's End storylines are all good stuff.
There's more intelligence here than the vast majority of horror films. The issue of what's reality and what's in Neill's head is left nicely open: 'Reality isn't what it used to be!'
What's not so good: The reveal isn't as good as the build up. Other films have this problem too, of course. By far the best bits of the Kubrick version of The Shining are the shots of the boy cycling around the hotel: you know something horrible is going to happen, but not what or when. In contrast, Jack Nicholson finally going wild with an axe is amusing rather than frightening. Here, we're treated to some not terribly convincing wobbly tentacled beings which are supposed to send you insane just by looking at them. They don't.
The structure doesn't quite work. There's a fanedit that recomposes the film into a linear story, losing the occasional flashes of the other bits of the story, and it works much better that way.
The casting isn't quite right either. Neill does cynical investigator much better than madman, while Carmen is better asleep (or as a model head on an acrobat's body!) than awake. In contrast, Prochnow doesn't really get a chance to show his talent.
Overall: It's just a pity that it doesn't quite work. The 'it can't be true... but it is!' genre has produced some better films than this and similarly the twist has been done better too. Part of the problem is that no-one's done a good commercial 'Elder Gods' type film. The best effort is from the H.P. Lovecraft Historical Society, who were behind the 2005 b/w silent Call of Cthulhu, and no-one's going to spend $20m on making that.
This has a surprisingly high rating on IMDB.com, so clearly there are people who appreciate it more than I do. It is certainly striking and memorable, but I'd just like it to be better.