I'd rather not see Hayden Christensen in the ST, more because I'm hoping the ST isn't as Vader-centric as the rumor about him seems to suggest than because of any bad feelings about Hayden himself. Natalie Portman was just as bad as he was in the PT and she's amazing in other stuff, so I don't find it difficult to believe at all that Christensen would do all right with good direction. One of the things that excited me most when the ST was announced, though, was that we'd presumably finally be moving beyond Vader (given that, y'know, he's dead). Setting up Vader as an in-universe influence on Kylo Ren is a pretty cool way to tie this new stuff into the larger mythology, but actually having Anakin Skywalker/Darth Vader literally present is too much. That said, if they come up with an anthology flick where Hayden makes sense, I'm all for it. Prequel fans deserve to be thrown a bone too, I'd just prefer it be thrown elsewhere in the timeline.

I really hope he isn't a Force ghost, though, because being forced to use the SE Jedi in marathons would be intolerable.