I've been watching the Star Wars saga with the Rifftrax commentary appended (the only way I can stomach the PT is when it's being mercilessly mocked).
I've just started Ep. 6. My analysis so far:
1 isn't that great. 5 is ok. 2-4 are absolutely hilarious. Looking forward to the comic hilarity that 6 is sure to bring. (That being said, I'm surprised that, given the popular view that 1 is the worst of the PT, the Rifftrax commentary on that one just didn't measure up to 2-3.)