Fallout: New California adds an all new story around a new player character, an adopted resident of Vault 18, embarking on a journey through the wastelands of the New California Republic's Cajon Pass. An unofficial prequel to New Vegas, FPB adds hours of new gameplay and a fully voiced stand alone campaign.
I have put a lot of hours into this mod. At the beginning when you are in the vault it's just the coolest things ever. The voice acting is up to par with the actual game itself. I have had so much fun with it and I'm not done yet. I will say though it sometimes confuses you as to where to go and you may get a little bit ****** off.