I started watching it now (currently at the halfway mark of 45 minutes). I see they let Hall remain a drifter, and they kept his affinity for using soda cans as ammo. They made him the just-arriving hero, though...
In the book the foreman is an evil antagonist, too. And Hall is actually content with living his life and letting others live theirs, even if he is somewhat antisocial. But the rat-killing with the cans is more of a hobby done only for the fun of it (like the guy who appears at the start of the movie). And his revenge on the foreman's abuse is blown completely out of proportion by him (if not evil, he was at least somewhat touched in the head).
Am I right in believing you have not read that story recently? Just as I am half-done with the movie (which I wanted to watch, anyway), I also recommend to read the story (again, if you already have). It is my favorite from "Night Shift" out of the ones I have read (I still have to read the last two short stories). I have read "Graveyard Shift" three times already. I even bought the Spanish version only so my boyfriend could read that one story (he still hasn't, though; also, he understands English, but refuses to start a book in English; I think he underestimates himself).
By the way, I wonder if they could have filmed this movie now (without using a lot of CGI for the rats). Carrying rats by their tails, throwing them, using a water hose to attack them... Poor working conditions for these little actors...