For the most part, I'm not terribly annoyed with the voice changes but it probably helps I wasn't exactly in love with the original cast either, though it will still be odd not hearing some of them.

From what I've read, the choice to change the cast was simply SE trying to add more of a new spin on the game for a new generation of fans. This title is being made not just for classic fans but to bring in new ones as well and they felt they should do so with the VA work as well in some instances.