Vader had a reputation as the one who hunted down and killed all of the Jedi, but it turns out that the clones did that. Pretty much the only Jedi we "see" him kill are the little kids. He didn't intend to kill Mace, he just wanted to cripple him in order to spare Palpatine, who took over from there. He just wasn't the killing machine I imagined all those years. (Oh, he kills his wife. But she wasn't a Jedi, so that doesn't count.) I did expect to see him kill more Jedi Knights in ROTS, and maybe a few Jedi Masters. I will have to watch Ep. IV again, but I don't remember Ben telling Luke that Vader hunted down and killed all of the Jedi Padawans.