Despite the dark and depressing atmosphere of the game, if you work really hard, you can help transform most of the communities that you interacted with into much better places then they were before. Necropolis can re-discover engineering, the peaceful town of Shady Sands can transform into the powerful New California Republic, Modoc can become a major farming community, slavery can be eliminated in the Den, Vault City and Gecko can be turned into centers of learning and tolerance, the Potomac River can be purified, etc.
When you first traveled to the Hall of Congress district in the capital city of the NCR, you will notice a large statue of the Vault Dweller (your player character in the first game) displayed next to the congress building. It is really heartwarming to know that the children of the people that you saved back in the first game still remembers your great deeds.
In Fallout 2, when you traveled to Vault 13 you can talk to the intelligent deathclaws and the human refugees that live there and listen to their stories. Many of them are really touching.
In Fallout 2, recruiting Dogmeat from special encounter Cafe of Broken Dreams.