Couple of performances really stand out.
Tim Curry as Gabe, Dominic Armato as Guybrush, Sarah Hamilton as April Ryan and Jan Rabson as Larry Laffer.
Almost every voice over in Curse of Monkey Island is amazingly well performed. Also love the voice overs in Quest for Glory 4 and King's Quest 6. Same goes for Sanitarium and Toonstruck.
Worst voice over: Fable (the adventure game that is
)