Well, first of all, define what you mean by bad voice acting. Because, IMO, some of the one piece VA's are OK, but the lines they say make them seem horrible.
Do you mean that they do not sound like the japanese?
Do you mean that they have no emotion?
Do you mean that they do not fit the character?
Oh, and if Liz Ortiz is the one who does Amy from sonic X, Serenity from YGO and Chopper from OP, then yes, she does sound the same every time. I mean, when Chopper has emotian in the OP dub, it just screams Amy to me and I keep expecting him to say how much he loves sonic (sorry for the bad example)