"Not so much a movie as a guest list," concluded Mark Kermode, but then he doesn't really rate The Big Lebowski either.
Perhaps some of the characters here are a bit too sketchy and the plot somewhat roughly assembled, but the star cast does in fact adequately compensate for this - and I don't see why that should necessarily be notched up as a defect. (Clooney is goofily entertaining and McDormand almost moving, but Pitt over-eggs it a bit.)
We ended up feeling this was a more subtle and substantial movie than many of the critics have allowed. That's not to say there isn't a better one trapped inside it - the theme I'd have liked to see developed in a slightly more mature fashion was that of how members of the 'intelligence' community end up acting on incorrect assumptions and mis-comprehended information.