After the first 10 minutes of watching this I was bored to death and had no idea what was actually going on. There seemed to be lots of babbling about a 'book', which is mentioned many more times throughout the film. There was also lots of nonsense about satanism, with plenty of chanting and ranting thrown in. I ended up fast-forwarding through most scenes in the hope of something interesting happening. Eventually something interesting did happen, but as usual it was too little too late. In the climax we get some strange fish bowl thing called "the devils rain" which seems to contain tortured souls. I thought this was an interesting idea that had potential. The devils rain is smashed and all the souls (or devils, or whatever they're supposed to be) are released. They then melt away ala Street Trash in the church which then explodes. The explosion is quite cool - you don't see exploding churches in films every day. At the very end we also get a woman moaning in a tortured sort of way - I think the implication is that she's in hell, but I'm not sure. I should also mention the faces of the satanists/devils, they have white faces with blank eyes which looks rather disturbing.
I can't really give The Devil's Rain more than three stars because it is mostly dull and confusing. However it does have a few good elements that some people may enjoy.