Day 26 - Best voice acting.
This is one of the more challenging questions in this meme. Why is that? Because no game's voice acting is perfect! I'm assuming this is about English voice acting, but I'm not 100% sure of that.
Looks like I'll be brainstorming this out. Here we go.
The English dubbing was generally spot on, even if people complained about certain characters sounding off/weird. A good example is Atoli, but she actually sounded basically the same in Japanese. I also consider the Japanese voice acting to be really neat in the series, too.
I can't pinpoint a specific KH game that I thought had the best voicework, but I believe that the returning voice actors improved over time, if nothing else. I have a fondness for KH:BBS in Japanese and KH2 in English and Japanese, if you'd like a more specific list.
Tales of the Abyss
Lucky Dog 1 (Japanese only)
Although I don't have any experience with the Steins;Gate original game, I have to mention that the TV series has some of the best voicework I've heard. Hopefully the game has just as high quality acting.