Ever noticed in RPG games like Fallout: New Vegas that everyone you meet in the world tends to sound a bit.... samey? There's a reason for this - cost. Most studios tend to reuse the same 4 or 5 voice actors for most of the more generic NPCs.
Enter Brave New World, a mod that's been in development for some time, and has just seen its first public release. It aims to add unique, professional voice acting to over a hundred of the NPC's you'll encounter in the game, making the world feel much more real and immersive.
The mod won't overwrite the voice acting from the major characters in the game unless the voice acting was particularly poor, but it does replace the dialogue for the vast majority of NPC's with dialogue in the game. So for example, characters like Doc Mitchell, Caesar, or Legate Lanius are left entirely alone.
The NPC's that have been given new voice actors have also had visual changes made to their character to help them better fit their new voices, reinforcing the character and helping them "match the newly cast voice actors."
The mod has been four years in the making and is really quite impressive. You can download it now from Nexusmods.