The problem with Vader's dialog is that it is Lucas dialog, before being handed over to an editor.

If it had made the final film, it would have gone from:

Luke. Luke. Join me in the Dark Side of the Force. My son, it is the only way. Luke. Luke.

To this:

Luke. Join me in the Dark Side. It is the only way.

Its kinda like that deleted scene for Episode IV on the original dvds where Obi-Wan says "If my blade finds its mark, you will cease to exist, but if you strike me down I will become more powerful than you could possibly imagine."

First thing the editor did was snip off the first half of that.