Extreme reactions to movies can never be trusted and used to project how you yourself will feel about a movie. A 0/10 and a 10/10 are thus equally suspect.
Any time I've allowed myself to expect a 10/10 movie after reading such scores from people I've been let down. On the other side of the coin I know that Avatar is clearly better than 0/10. It quite simply would not have done the business it did if it was truly so bad.
I think our problem with judging others' opinions is we all use different rating systems. For example this side conversation was sparked because I called WWE's 5/10 rating out for describing a "bad" movie. That isn't a "bad" rating. It's somewhere between being "ok" and "meh."
Maybe a new rating system is in order. This will be mine:
0/5 - I hated this movie. I either turned it off or wished I had!
1/5 - I didn't like this movie. It was compelling enough to sit through to the end but was dumb and best forgotten.
2/5 - I enjoyed this movie but have no desire to see it again.
3/5 - I liked this movie and would like to see it again someday if its on Netflix or something.
4/5 - I really like this movie. I would like to own it someday if I can have it for a decent price.
5/5 - I freaking love this movie. I will buy it the day it comes out, will probably double dip to better releases that come out, will maybe own merchandise from this movie and will see it so many times that I can quote it word for word.
So with this rating system in place, here is how I would rank SW and Avatar:
ANH - 5/5
ESB - 5/5
RotJ - 4.5/5
TPM - 2.5/5
AotC - 1/5
RotS - 1.5/5
TFA - 2.5/5
Avatar - 0/5
I'm not being a movie critic when I give it a rating. I'm simply conveying how much I enjoyed the movie. I did not enjoy Avatar despite any of the good things that might have been in it. And despite the flaws that might be in a movie like Star Wars, there's really no other movie that gives me so much pleasure to watch.