BackStage.com has a feature article on “Actors Casting Directors Love” which mostly covers on-camera actors, but there’s an interesting quote from animation casting director Bernie Van De Yacht that I felt was worth repeating here:
[As] an animation casting director, I generally don’t try to narrow it down to whether they have voiceover experience or not. A good actor is a good actor, no matter what arena they’re acting in. Sometimes it’s a detriment if they’ve done too much voiceover work, because then they tend to sound a little bit cartoonish; sometimes the heart and soul is missing. And if somebody has never done it before and is just a really good actor and can create an entire world in a soundproof booth with a microphone, it’s amazing. It’s kind of like an actor on stage having to do a soliloquy, where they have to hold the interest of the audience by themselves and with nothing else and we have to be able to visualize what they’re saying. And I think that actors who are good at that tend to be very good voiceover actors. They’re the ones that excite us.