It all depends on how old you are and when you started listening to Metallica. Personally I was a big fan until the Black album came out, and even that album had some decent tunes on it, in my opinion.
I think that what gets the old Metallica fans is the fact that Metallica now seems to be everything that they used to detest and speak out against. This could be an endless debate that I'd rather not start, if you enjoy the new stuff great, but just respect the fact that the old Metallica fans have a point of view as well.