I thought Agrippa's voice added some contrast to all the other serious voices. His was light and friendly, which I found hilarious being that he was basically a zombie XD
When I first met Agrippa, I really hoped to take his head with me and he continue talking to me, sorta like Red and Clarence.
I agree with Unreal. I think Agrippas voice fitted the part even though he liked to talk a lot.
What sometimes baffles me is how good the voice acting in both Amnesia and Penumbra generally are compared to big and expensive titles. Something I hope to see in upcoming games, more interesting charatcters with great voicing.