I have not read the novel this movie is based on, but judging the movie by itself, when the credits rolled, I was thinking: "Uh, so that was it??" The plot is shallow, and the acting is so-so. Quite possibly this is partly due to the fact that many of the character's motivations either remain obscure or are difficult to believe. Hackman turns in a decent performance, as he usually does, he has a good scene with Dunaway, and a number of good lines with O'Donnell. On the whole, Dunaway's character is paper-thin, and not terribly useful to the story. O'Donnell does not have the range to pull off his part, which probably adds to the monotone of the story.
POSSIBLE SPOILERS BELOW But the weakest part is the story. As told in the movie, it is without any surprises whatsoever. Obviously, since it's a Grisham movie, we assume that nothing is quite the way it seems, but ultimately it is pretty much the way it seemed from the beginning, with a few additional details that had been swept under the rug by the powers that be, for obvious and totally unsurprising reasons. No drama, no suspense, no surprising plot twists, nothing. The grandson of the bad guy is digging around in some old files (including the sneaking-into-the-archive/library/storage scene, which in this movie passes without any tenseness whatsoever), connects a few dots that provide a little bit of background to the crime in question, but that's about it. There is a faint hint at larger-scale intrigue, but it is not elaborated, and remains entirely inconsequential to the viewer or the characters (well, except perhaps the guy on death row).
Watch it on a Sunday afternoon for Hackman, and perhaps Lela Rochon (as yet another useless character) as eye candy.