Altman, but mostly Elliot Gould being fantastic: the rambling internal monologues are a great device to bring text to the screen. The opening scenes with the cat are classic. Mr Precious Bodily Fluids (Sterling Hayden) is solid as a Hemingway clone. That would be Arnie putting in a cameo as the muscle in the office. For all of this I couldn't imagine reading the Chandler original.
This is not the best Altman I've seen (that was probably Shortcuts) but it is still damn fine.