A really quick read, almost a puzzle. 
 Initially, I found the dialogue stilted but it soon became clear that this was just a refection of the participants' formality on first meeting. 
 The book sped by and, at various points, I suspected everyone. The 10 characters were well-differentiated and I had few problems remembering who was whom. 
 I was a bit disappointed by the resolution as it seemed somewhat arbitrary. (view spoiler)[ A number of the victims could have been the 'red herring' since it involved collusion between the murderer and an unsuspecting member of the other 11. Also, when the murderer eventually kills himself lying on the bed, wouldn't there be much more blood on the pillow than if he'd been shot elsewhere and carried to the bed after he was dead? (hide spoiler)]