I agree with you Brice. Name recognition doesn't make a great character. Neither does a great performance I would like to add. Take Nicholas Cage's performance in Leaving Las Vegas. That was a great performance, but the character itself isn't. In fact, the character got lost in the performance itself.
What makes a great character is memorabililty, longetivity, and making people CARE about the character. Love or hate, the audience cares about great characters long after the film is over. Take Connor or Duncan McLeod, Indiana Jones, George Bailey, or even Kikuchiyo from Seven Samurai. Those are great characters that people think of years later. True, the actors portraying them did good jobs, but it takes more than a good or even great performance to make great characters.
Vader has that, in my opinion. George Bailey has that, as do Vito Corleone and Indiana Jones and Snake Plisken (sorry, watching Escape From L.A. right now). I'm NOT saying Jack Nicholson's character from OFOTCN isn't a good character, he is. Not saying his influence isn't felt even today, it is. I'm just saying that I felt, and always will feel, that Vader is a much, much stronger character than Jack.