[lepton]

Revenge of the Lithp was weak!! Why would a Jedi trained since birth change overnight because of a dream??

He wasn't, and despite the complaints, he didn't. I will concede that the relationship with Palpatine was implied more than revealed, but there are a lot of steps towards his turning.

[Betaille]

"but there are a lot of steps towards his turning."

Not in the movie there aren't. He changes his mind 100% in a matter of minutes with no feasible explanation.