Huh?
Obi Wan knows Anakin is the father of Leia and Luke, and also knows who/what Anakin became. Why wouldn't he flat out lie to Luke about his father in an attempt to protect him?
The Vader-Luke plot twist has made perfect sense since 1980, and now it doesn't because it's just too obvious, as you put it?
It's one of the annoying things about movies these days and particularly Star Wars. It worked in ESB because back then it was a lot easier to surprise people with such a plot twist. Now it's been done and so have several different plot twists so it's almost impossible to really surprise an audience. I say "particularly Star Wars" because with the internet these days you have so many people discussing every conceivable plot point going forward, so now when one of them actually happens it will be referred to as "lazy writing".
Agree regarding modern day plot twists, but that's completely beside my point.
Vadar and Anakin were two completely different characters at the time A New Hope was released, *and* even in the first draft of Empire. It was only during the rewrites that the (absolutely brilliant) plot twist was conceived.
My only point is that in ANH it's very obvious that they were not written as the same person in Obi Wan's dialogue. Can't quote it exactly, but he very distinctly addresses them separately in one sentence.
On a similar note, he also directly addresses Vadar in his showdown as "Darth", twice. Again an example not of lazy writing, but re-imagining the material. Darth only became a 'title' when Darth Maul came about.
Lazy writing, now that's the prequels and ROTJ somewhat.
