In fallout 3, I loved the RPG bits of it, but there were a few lacking things that are probally well known.
1. D.C is not a warzone. I don't see mutants fighting anyone in the mall. They have their lazy yellow asses on the trenches while talon company runs around firing their weapons into the wall. I would have liked this area to be a little more developed in the next change of scenery
2. Dialogue is pretty boring. Some of it linear. Changes to it would be nice.
3. Customization would be nice. Not necessary , but would be nice.
4. A variety of environments. Not just repetitive caves and interiors.
5. A larger variety of weapons and scavenging.
6. BIGGER TOWNS AND MORE QUESTS- Biggy
7. Factions that I can OFFICIALLY join, do missions for. Even wear the uniform and all.
8. Realistic encounters. (Etc. A raider attack, random mercenaries attacking a small settlement.