I have to disagree with my distinguished colleagues reviewing below. I rented and watched this last night based on the recommendation of a friend.
It is a good if somewhat contrived story, well filmed, but is undone by a poor screenplay that has dozens of holes. The acting includes good performances by Amy Ryan and Ed Harris, and some nicely done minor roles, but unfortunately, Casey Affleck in the leading role doesn't have the acting stones to carry the complexities of his character, particularly in the climactic sequence.
Ben Affleck's directing debut is competent, but uninspired. He shares the screenwriting credit, so I'm not sure how much he is to blame for the script, but he has to take some for the continuity issues and the internal logic holes in the film.
As to the widely touted twists and turns of the plot, they're over-rated. I watched it with my eighteen year old son, and by the time the quarry scene had ended we had figured out about 80 per cent of what was to come.
I have a hard time understanding the critical praise of the movie. Its not a total dud, but its nothing at all special.