Man o man. Video game voice acting. I don't know where to start.
The first MGS had the best voice acting in the business at the time, a big part of what made the game so great. The voices were perfect, especially for Snake, Ocelot and Liquid, and the delivery was perfect. One of the main reasons I loved Liquid was how perfectly his voice fit. I think David Hayter does the voice perfectly for the games. He might not get EVERY moment, but I can't imagine anyone else doing his voice. Except his Japanese counterpart, who is also great.
Then, we got MGS2, some pretty bad voice acting here and there.
However, MGS3 took the cake. Some of the worst voice-acting I've seen. Considering the high caliber of the game, that only makes it much more unforgivable. Snake was okay. But his mentor, EVA, the villains, especially Volgin, all had HORRIBLE voice acting. I was so disappointed. Especially since you can easily tell the Japanese version had perfect voice acting from the trailers. It's a shame there was no option for dubs.
Another that could have used that option is FFX. Jesus christ did Tidus and Yuna suck ass. At least FFXII redeemed that overall, everyone had great voice acting (except the whiny main character, but I pretended he wasn't in the game).
I thought the Fear Effect series had great voice acting, I loved the characters in that one.
I agree with a lot of the ones already mentioned. The Jak (of Jak and Daxter fame) games had great voice work. Grim Fandango takes the cake for me.