I remember when I first rented this movie from Blockbuster when I was eighteen. I had just started seeing R-Rated movies with a clear conscience and I had also discovered the Independent film industry. There were a lot of movies that were fundamental in this - Usual Suspects, Fargo - but this film was special in a way I can't explain.
I've always loved the work of Sayles's films - I've seen several of them since then - I think his films are among the densest of any American filmmaker since Robert Altman when it comes to ensembles and storytelling. There are at least four plots going on in the present and three in the past and yet I was able to grasp them all from beginning to end. This may have been the first time I ever saw Chris Cooper act and while he's given better perfornances this is one of his most humane. And I should also mention this was the first movie I saw the potential of Matthew McConaughey rather than the sex god he became later on (which he does well, I grant you) McConaughey cut his teeth in the indie film industry and I always thought he did his best work there in so many films - Frailty, Bernie and so on.
Sayles has often shown a leftist politics in many of his best films: Matewan and Eight Men Out show that at times - but he keeps his politics subtle here and lets the story carry itself. Even when we learn the truth of the killing it seems not climatic but almost underplayed. I also agree with you about Joe Morton: this is the best film work he's ever done.