The first half makes you think it's a real movie...

Rating: 4/10 (13 July 2007)

And then Cheech shows up and all the great rising action just comes to a halt. Cheech is effortlessly hilarious from what I remember, but you'll notice he doesn't fit at all. The rest of the movie takes a quick turn to stupidville immediately after that. It's not done in a funny or entertaining way either. It's just lame.
For the sake of laziness I save the basic synopsis to the other reviews, but I want to point out that this movie actually had quite a lot of real potential in the beginning. Keitel's character and his loss of faith, his love for his kids, etc. could've played against Clooney and Tarantino's bond and it would've been compelling despite Tarantino's inability to act.
Unless it's entertaining for you to watch a movie get sabotaged half-way through you should avoid this one. If only the first half had been so terrible--there was actually a touch of substance for once in one of Quentin's movies, I should've known it wouldn't last--I would've turned it off then and not wasted my time.
The "4" rating is mostly due to Cheech Marin's 30 second onslaught of hilarity and the acting chops of all but Quentin in the beginning. They're so good at their craft that I actually thought for a minute it was an attempt to really say something.