First, what I like about Fallout 3, and what I hope will continue on into the next Fallout release:
-Pipboy: Easy to use, in my opinion. I also enjoy being able to freeze combat and change your equipment instantly. Very useful.
-V.A.T.S.: Helpful when being overwhelmed by many enemies. Gives the feeling that I am trained for combat and not just blindly throwing myself into it.
-Character Options: From customization to dialogue, this gave the player some sort of say in the progression of the story.
-Companions
-Camera Perspective Options
Now, what I would like to see in the next Fallout:
-New location: Many posters in this thread have mentioned other international locations. Also, how about other time periods? History often repeats itself, so how about something futuristic after civilization has begun rebuilding itself? Maybe another nuclear threat, or something else entirely. Or maybe fallouts in the US are needed again while the main character is elsewhere, leaving him behind (well, not entirely! You still need other characters )
-Character Interactions: As said in previous posts, choices that allow you to see the true consequences of your decisions would be great. Also, more intimate relationship options would be nice without them being raunchy. I liked the idea someone mentioned of a fame or notoriety level, and also the idea of camouflage within groups while wearing their clothing (much like the ghoul mask in Fallout 3.)
-Career Tree: So you want to make your character a mercenary, a trader, a relentless gunslinger? Make the option actually available with special interactions and quests. Let the player character be recognized within a certain career realm. The G.O.A.T. is not enough.
-Character Customization: It was difficult to see clearly the character I was creating at the beginning of the game, and I still felt a bit limited in some senses. Armor should be customizable. Repair isn't just for weapons and quick fixes - it could be used for improvements and advancements. Whether its completely free form or schematics related is up to question.
-Interactive Puzzles: I have to break through locks and hack through computer codes, but when it comes to Megaton's nuclear bomb I just "choose" to disarm it and ta-dah! We're saved! How anti-climatic... At least let us puzzle fiends connect and disconnect some wires. Players should feel like they're actually accomplishing something, especially when it comes to the important stuff.
-Level Cap: Level 20 is too low! Give us some room to grow.
-Map: Larger map, more towns/settlements/cities, more characters, more opportunities! Of course we all want more, but can you blame us? Let players take an active part in cities. Maybe let them run for counsel or study under an influential town figure so they can advance to a higher rank and gain more recognition within the town. Maybe allow multiple homes. (And possibly something similar to a family dynamic.)
-Platform Fairness: Don't leave PS3 users in the dark when it comes to expansions!