I've never read any Dostoevsky before, although I'd had friends who had read 'The idiot' for year twelve english literature. Needless to say I read with trepidation...
Basically it seemed to me the book was the rambling of a journal by a man who didn't seemed to fit with the world. There was a distrust of everything yet at the same time wanting to trust.
The book was split into two sections the first was just a monologue while the second told stories in some way explaining the first section. The second was a much more entertaining section. It brought the whole novel to life.
The wikipedia (see above hyperlink) suggests that the novel was the first existentialist literature. I suppose for most of us living now this is just taken for granted that we are individual and create our own destiny. Certainly I would think this is part of the American dream of been 'self made'. I can see this theme coming out in the book, 'the man' the narrator never been able to grasp it. I could image that when read by most Cultures of the early 19th Century this would have been a foreign idea existentialism, especially within the lower class.
Overall I thought it was a difficult read, because there was probably much more behind the words than I actually grasped.