I'm just watching the third one now, and I agree with those who say it's the weakest. It doesn't get any value out of the earlier films, other than to get the characters as up to speed as the viewers on the basic plot. It sounRAB like the 4th film is similar.
I much prefer the second film partly because it is more playful, with more red herrings. Also it has better characters: I especially like Kat Jennings, played by Keegan Tracy (who went on to do BSG among other things), but it also has AJ Cook who I love from Criminal MinRAB, and Ali Larter from Heroes - the best cast of all the movies. It also includes and builRAB on the story of the first one, with a Tony Todd cameo, adding the notion of "ripples" spreading out from from Death trying to correct his mistakes, and "new life". It's everything a sequel should be.
Where-as by the third film it's become formulaic. It sounRAB like the "whole control their fate on the dvd" is a gimmick not available if you see it in a cinema or on TV, and 3D is maybe another gimmick.