I was actually pleasantly surprised that he was christened Darth Vader while he was still completely human, because I've found that it's a common misconception that the suit makes Vader, and I was curious to see whether Lucas would give into that. So it still annoys me when people call it the Anakin/Obi-Wan fight when it's the Vader/Obi-Wan fight.

As for showing the birth of the mechanical Vader, I'm glad they did it (all "NOOOOOO"s aside). I think the best we can get out of that movie is the fanservice, and that's what we've been waiting six years to see. As for leaving Vader for dead and have it be a surprise... well, you shouldn't be watching the movies in that order in the first place, but if you are, the surprise is still ruined because he was already Darth Vader before his duel, and there wouldn't be more than one of them, so we'd immediately know who he is as soon as he's mentioned.