Actually, I would say a big number of adventure (point-and-click) games feature great voice acting (especially considering the amount of dialogues). Like the Monkey Island series (except 1 and 2 of course), Broken Sword series, Grim Fandango, Indiana Jones, Day of the Tentacle and so on.
One game I don't think many people will mention is Ghosthunter for PS2. It has SURPRISINGLY good voice acting, in that it doesn't feel like actors are struggling and it has a nice flow to it. Could be because of the script too. Sure, the game doesn't feature an epic storyline or anything like that, but the voice acting is really good nevertheless.
In general, Western games have better voice acting than Japanese translated games. I think this is obvious for a number of reasons. Western games have the script made in English (well, with some exceptions) from the beginning, the voice director has a more accurate understanding of how the lines should be delivered, and some parts of Japanese games have too much Japanese culture to make much sense in English. And since the lipsync in Japanese games is made for the Japanese language, it can put translators and voice coordinators in an even tougher position.
And the worst voice acting I've heard in a while was when Snake (David Hayter) tried to laugh in MGS3. :lol
