I didn't have a problem with the prophecy or the 'ahem' virgin birth.

This is a universe with people able to see the future (but always open to misinterpretation) as an established fact from the OT.

It also has clones and the like so inserting a corn-ear into a unploughed field shouldn't be too much of a problem.

The two Sith thing isn't a biggy for me either even if the EU authors went out of their way to pretend it never applied to them.

A good writer would acknowledge the prophecy and then make it clear the Jedi are divided as to it's value and meaning and show us it's being taken advantage of by a canny manipulator/s, like Paul in Dune.

Which seems to be what Lucas wanted to do but in the end all he actually did was throw it at the audience and then change it in the last episode (so is it bringing balance to the Force or destroying the Sith???).

The end result was to make the Jedi look even more stupid and give Mace an excuse to contribute to one of the least likeable fictional personalities in any medium by constantly goading Anakin, isolating Anakin, not including Anakin and never trusting the confused plank.