Ewan McGregor has always been pretty upfront that he thought the prequels weren't as good as the originals. He's gotten in trouble a couple times because of this.

Terrence Stamp bashed Episode I. It seems he expected to actually be acting, instead of reciting lines to a wooden post in a blue screen stage.

Liam Neeson was so upset after the preview of Episode I he ranted that he was giving up acting forever because he couldn't stand the crappy movies he was being put in (that year, he was in both The Haunting AND Episode I). He later reconsidered.

Hayden Christensen has been very diplomatic, but he's said that he didn't get the script for Episode II until the week before filming and he was really worried that he wouldn't be able to make it believable. According to a less reported anecdote--but highly believable one--his reaction to a friend was "I'm fucked." And he was.

Interesting that Daniels would have negatives views. In mean, understable, and he's always had a sort of "complicated" love/hate relationship with the series, but I hadn't heard him be completely honest before.