My list (best to worst):

1. Three-way tie:
Star Wars (1977)--8/10.
Star Wars: Episode V - The Empire Strikes Back (1980)--8/10.
Star Wars: Episode VI - Return of the Jedi (1983)--8/10.
2. Star Wars: Episode III - Revenge of the Sith (2005)--7/10.
3. Star Wars: Episode II - Attack of the Clones (2002)--6/10.
4. Star Wars: Episode I - The Phantom Menace (1999)--5/10.

Maybe I'm being stingy. Ah, George, too bad you didn't cast better actors in some of the key roles. Other complaint: stiff dialogue (seems to be a staple of many post-Star-Wars space opera productions--ugh!), which the writers of The Simpsons have also noticed (see the spoof in which the Star Wars plot is solely about bureaucratic procedure).

1. New Hope
2. Empire Stirkes Back
3. (tie) Return of the Jedi / Revenge of the Sith
4. Attack of the Clones
5. Phantom Menace