I have said this many times but in fairness to Lucas, did anyone expect the PT to be as good as the OT? The key to any movie (IMO) is characters, if you don't have great characters, and don't care about the characters, then everything else doesn't work.
I remember telling my friends (who were juiced for the PT) in the spring of 99, that the PT wouldn't be as good as the OT because I don't think Lucas is going to be able to create another round of lovable characters. The OT cast is magical and like most great movies it is lightning in a bottle that cant be duplicated. Han, Luke, Leia, Chewy, Obiwan, R2, C3PO, and Vader, those characters are iconic, and fans cared about them. For great characters to succeed you have to have chemistry, you have to have to hire the right actor for that role, there is ALOT of luck involved.
Now you're asking Lucas to create another trilogy with iconic characters that equal the OT characters? It was never going to happen, because if it did then more sequels were be great.
I more amazed that ESB is a classic then the PT not living up to the OT (IMO), because the odds of making a great sequel/prequel that equals its original are very rare.