Stagey but quite watchable
The best way to view this is to think of it as being a stage play rather than a film. I.e. it is low budget and script driven. It keeps you guessing about what is going on. The plot twists and there are lots of false leads about what is going on - criminal or supernatural, it keeps you guessing.
Plus it's sort of funny to see Alan Ford do an over the top version of his Brick Top character from Snatch stuck in the middle of a mystery and totally out of his depth.
I'd compare it to The Usual Suspects in fact.
http://www.imdb.com/title/tt0118604/board/nest/45170697?d=124482056#50057239