I have to make a few comments, hopefully not too bad. It's been a long time since I've watched the show.
Ash's voice - Sounds rather sarcastic most of the time. Ash's appearance also doesn't look like the voice would fit how he acts. His voice also stays rather monotone, and the pitch changes every now and then. They seriously should of kept Veronica Taylor. That lady's a master piece.
Hikari's voice - Fits Hikari well. :] A bit squeaky and unpredictable, as well as monotone a few times like the other ovices, but overall, it's good.
Piplup's voice - I loved the Pochama voice.
Piplup's voice fits its American appearance, but the sarcastic moments with its voice seems a bit too cute.
Professor Oaks - I loved his voice. It fit the old geezer well. Now he sounds like......a squash?
More later on me. :/