I always saw Vader as a true BAD GUY through and through in parts 4 and 5 (that's why we loved him so much!). What I saw in the current movie was just some brooding, less than imposing, chump; totally taken by Palpatine. I think the emperor would have to use some serious "tough love" on the current Darth to mold him into what I saw in the earlier movies. Steyn was right on in his criticism of the whole Anakin to Darth transformation.
Also, WHY WHY WHY did Lucas put Christensen in the Vader costume?!?!? There was no need. He's not supplying the voice even. Hayden is way too physically unimposing for the suit. The guy that was Vader in parts 4 and 5 was an ex-weightlifter that stood like six-five or six-six. In the current film, Vader is barely taller than the hunched over emperor, even with the helmet on! This may be a quibble but this really bugged me. It's like Lucas thought he "owed" Christensen the chance to wear the suit, no matter how ridiculous it looked!