I wouldn't recast Portman, Neeson, MacGregor, or McDiarmid. They had the appropriate look and persona for each character (and of course, IMD had already established the Palpatine character, so that was a shoo-in).

I didn't have a big problem with Samuel L Jackson, but what always lurks with him (as well as Robert DeNiro) is the fact that the single character he often plays seems to come through every role he ever plays. I think the concept of a high-ranking council member sort of skirting the edges of the dark side, as explored in EU stories, is incredibly interesting; unfortunately, the PT story wasn't Mace Windu's story. It would have been much better had Windu's character been replaced by a more orthodox Jedi. But if you're going to keep Mace Windu, probably better to go with a different actor with a less pervasive, less familiar screen presence.

Anakin? James Franco, perhaps? He was a very minor blip on the radar when Clones was filmed - and I think the unfamiliar touch was necessary for Anakin. I think he's a pretty good actor, and I think he can definitely play dark better than HC did.

The voice actor for Watto was pitch-perfect. One of the very best characters from the PT, IMO.

Bail Organa? I think Jimmy Smits did a pretty good job - I just have this anti-Jimmy Smits thing. I just can't see him as some intergalactic person of importance. As Rod Hilton so precisely put it, it's Jimmy fucking Smits.

Pernilla August did a good job. Temeura Morrison wasn't terrible, I guess. He had a tougher job than most of the PT actors IMO.