Anyone knows why the original voice actress didn't retain the role?

Can be anything really. Her scheduling didn't match, she wasn't available or didn't get enough pay for the role.

The voice actress in Witcher 2 is AMAZINGLY AWESOME in the character though. She gives Triss so much personality that feels totally genuine and is often hilarious. I love the way she laughs when Geralt wakes up with a hangover and a new tattoo.

I personally don't like the new one as much. The first actress sounded very "womanly", whereas this one sounds much more like a girl.

Granted, some of the first Trish's dialog was not delivered well, but the qualities of her voice fit the character much better than the new one in my opinion.

I think the new one speaks too softly.

Her appearance was changed hugely as well, so I imagine the new actress was hired to fit the new look and take on Triss.

Have barely played, but I like the new character as a new character...not as Triss, though. TW1 Triss was so endearing...this one seems to lack all that.