Sure every movie has flaws... but good films outshine their flaws by a lot of good stuff. I don't think the PT as a whole does. And it's not just sentiment, there's a lot of stuff that absolutely makes no sense in these movies.
Take AOTC for instance... I have said this several times before, but it's a valid point I think.
When AOTC came out I liked it a lot better than TPM which I thought was wooden, slow and had an awkward angle (taxation of trade routes... WTF???). It had good bits but it simply lacked content. AOTC however was interesting: a detective story (although OB1 is not much of a detective), the introduction of a sinister Syfo Dyas as the mysterious Jedi that ordered the CLone Army whcih in turn would lead to the infamous Clone Wars (finally!!), the appearenace of Count Dooku. and the love story that would lead to Anakin's fall... It sounds interesting...
However... all the leads in AOTC lead nowwhere when ROTS came out: the whole business with Jango, the bounty hunters, the 'detective story', Syfo Dyas.... it all vanished... Jango was mere exposition of Boba (boring and completely obsolete), Syfo Dyas disappeared from the face of the earth and Dooku was killed off right away... it made AOTC, though it looks lovely, completely nonsensical: it tells us nothing we need to understand the Clone Wars or Luke's story or whatever... That makes it eye candy.
Who cares HOW the cloe army came about... it's not crucial to understand the Skywalker story and actually... we still don't know how it came about since Syfo Dyas was no longer an issue...
The only crucial element, the one we really need to understand and feel along with the rest of the saga, in AOTC the Love Story of Anakin and Padme... and that, AGAIN: the only relevant plot point from AOTC, was so badly done, it's totally incredible and lends no backing to OB1's remark in ROTJ about the 'good man that was once your father'. When was that??? When he was ten??? OMG....
That makes AOTC mere eye candy. It even makes TPM better even though it still is quite wooden and boring...
Leaves us with ROTS: many good things, pacing, humor, plot turns... all pretty good.... up to THE moment the prequels were all about: Anakin's fall.... Rushed, incredible, messy build up and a pretty lame OB1/Padme/Anakin scene on Mustafar...
These are arguments that IMHO transcend liking it or not... These failures make the difference between the classic that the OT was, with strking moments like the 'I am your father' scene... and the okay-prequels of the Star Wars saga... It misses out on the crucial moments.