Voice acting to me seems very underrated, even by myself. But it can really set the mood and make a game shine above all others if the right voice actors are used. Their have been two points in gaming that I have been wowed by the voice acting, Eternally Us with its unparalleled voice acting from all of its characters, and Sharon Mann in all of the games I have played with her in them.
Sharon Mann is an amazing voice actress, my personal favourite, and is very unknown (I cannot even find a list of all of her voice acting jobs). In addition to Syberia I have also played the Return to Mysterious Island & Return to Mysterious Island 2: Mina's Fate games (based off of Jules Verne's novel The Mysterious Island) in which she voices the female protagonist Mina. Great games, made even better by her voice acting.