Saw this yesterday. I'm not much of a Val Kilmer fan but I like much of Mamet's work, so I went to see this. Kilmer is excellent, the script is tight and terse, leaving lots unsaid but with enough information to allow you to connect dots and draw inferences.
The first 80-or-so minutes are riveting. Then it starts to unravel. I don't think Mamet knew how to end it but, being Mamet, got away with it.
Those first 80 minutes, though, make the limp ending tolerable. Worth seeing.
FPW