Well yea, pretty much my thoughts, as well :)

One can "like" a seriously "flawed" product for, I think, two very basic reasons:
-the flaws have some sort of appeal in themselves
-you don't give a crap about the aspects that are flawed, at the moment.

Like, recently, I watched Dark City, and I just couldn't be bothered to follow the plot line closely (couldn't understand some of the dialogue), nor did I feel a particular connection to the characters (the whole "stoic" "noir" atmosphere might be at fault - everyone's talking as if they're stoned).
So the only thing that kinda disturbed me were the sometimes narmy aliens and Sutherland's speech pauses, but I enjoyed it very much for its setting, its mysterious setting, and the imagery.

Did the protagonist have a very good arc? I don't even remember, but it was a hell of a payoff.

So if someone watches the prequels, and just doesn't give a crap (like, by going to the toilet while Ani and Ami beat around the bush), then hey, who cares.

I just think it's wrong to say that they could be considered good movies if you only thought away the OT, for the reasons stated - but yea, at the end of the day, if the flaws don't go over the head, then you're pretty safe. ;)