Mud is a first-rate little drama of life among the lower classes, a little like Winter's Bone, and maybe a good deal more subtle than it seems at first glance.
Fourteen-year-old Tye Sheridan is a lot like Matthew McConaughey, in both have a tendency toward violence in defense of women who don't much reward it (and McConaughey's "father" may be right in thinking Reese Witherspoon isn't worth it), both may be a little too attached to life in a decaying world along a river that is doomed to development and both may be too given to following impulses instead of using thought at caution.
Sheridan's buddy Jacob Lofland is much less eager to get involved with McConaughey-- who is hiding out from a murder charge and whom Sheridan and Lofland don't know at all-- and Lofland knows better than to run in a woods full of cottonmouth snakes.
Sheridan is sure he knows what is the right thing to do, but he certainly doesn't seem to have chosen the right woman, and he eventually lugs Lofland into even deeper involvement in dubious activities than he gets into himself.
I'm not sure writer-director Jeff Nichols intends all these warnings against his 14-year-old protagonist, I think he's just after the kind of complications real life always confronts us with. McConaughey's instinctive ability to relate to kids in the middle-teens seems sympathetic, and except for the posse we see that seems to prefer to bring in McConaughey dead, there are no villains in Mud.
McConaughey's "father," Sam Shepard, and Sheridan's father, Ray McKinnon, are rough but clearly good at heart, and probably right in their judgments. McKinnon's marriage is breaking up, but he insists that Sheridan not blame his mother-- it's just the river life that's too much for her. And it doesn't seem to offer happiness to anybody.
But Mud does-- to anybody who loves grownup character drama. It's been called the best movie thus far this year, and may well be.