I have never been able to get through the last one (part 3) without falling asleep. I went to the theater three times, have it on dvd, and tried to watch it a number of times, even transferred it to my laptop to watch on a flight to Portugal, and still fall asleep. I don't even remember the opening credits...
I doubt i will purchase it on Blu ray yet.. just going to wait for the inevitable 3-D release to come out in a few years.