I've read a few of the other user comments about this film and often words and phrases like pretentious, dull, boring, lacking in entertainment are used. All fair comments, it is definitely not a film for a fantastical exciting escapist experience - however, I would suggest that a little effort on the part of the viewer will pay big dividends.
The first thing to say is that the actual plot of the film is not the main focus of the film. This is all about the madness, and subtle questions that are raised and need to be held in your mind throughout.
Every scene provides vital information, but do not forget we are seeing inside the 30 or 40 year old memories of a man who has spent most of his life in a mental asylum. I would not advise taking any scene at face value, particularly the flashbacks.
It is a challenging film and may at first seem to lack coherence, or be artsy for the sake of it. However, like the jigsaws that appear in the film in various forms it is the final pieces that are the hardest to deal with and potentially the most dangerous.
And at the end we are left with a question - is Spider's trauma the cause of his insanity, or is his insanity the cause of the trauma.