Red Superfly
You creepy little stalker
I'm not sure how to take it actually.
With Vader - ROTJ gave him his face. ROTJ Anakin is what I see behind ESB Vader's mask. Prequels haven't done anything really in that respect. I picture Sebastian Shaws face behind OT Vaders mask, not Hayden, because in ANH & ESB he would look more like Shaw.
Boba Fett? Yeah. The prequels have changed him in my eyes. Given him a face he never had etc - but I personally don't like it. I actually preferred it when Boba was the cool, brooding, faceless mystery - "the man with no name" as Lucas once himself called him. I don't like how one of my favourite characters has been cheapened because he has not only lost that brooding sense of mystery - but the face he was given was that of an annoying high-pitched little brat. He has about as much "brooding" as a fluffy bunny.
But that's just me. Vader hasn't changed because of the PT, while Boba isn't as cool as he used to be because of the PT. I'm sure there are many out there who think Boba being pushed into the limelight adds to his character - I simply see it as exploiting an over-rated character to please the fanboys, at the expense of the character itself.
I would wish we hadn't seen Boba at all, like Han Solo - there's no real place for him until the OT.
The PT does make me see it in a different light, but I personally don't like it, which is why I'd recommend for any newcomer to watch them 456123. At least then they'd get what I consider the best version of Boba Fett and Darth Vader. For at least three films.
Boba Fett and Darth Vader's characters are probably the two best reasons as to why watching the entire series 123456 simply does not work.