That's odd, I thought they did a way better job with the voice acting in the 2nd special edition, especially with the timing. I thought the MI2 special edition overall was much more polished than the first one, I guess since they learned from their mistakes the first time around. The only voice actor I wasn't that happy with was Largo, but other than that I thought the cast did a decent job.

As far as Curse of Monkey Island goes, I think there are 3 main factors that made the game feel different from the previous 2. 1) None of the 3 principal guys (Gilbert, Schafer, and Grossman) were involved, 2) Voice acting for the first time changing the way we looked at the characters (kind of like how everyone thought Mario sounded like a guy from Brooklyn until Super Mario 64 came out), and 3) Bill Tiller's art style (check out A Vampyre Story, which he directed; it has a similar look).

You need to check out the Tales of Monkey Island series. I know Dave Grossman was involved, as well as Jonathan Ackley and Larry Ahern from CoMI, and I believe Ron Gilbert was kind of a consultant on the project as well and came up with some of the new characters (not sure if Tim Schafer was involved or not).