character's speed: A character in an open world game should be able to run a lot faster.
blood effects: The vats is great and should not be changed. The blood and gore need to be touched up. I had a problem killing people because of the sound it made when blowing off a face. I also thought it was realy poor that you blew up a person by shooting them n the legs with a shotgun. The amount of gore was fine, but it was awkard. It would be nice to slice someones throat and perform stealth kills. I would like to see and here the blood leak from the enemies body. It would also be nice to have the blood stain the player's clothes in a realistic way. I think it was disapointing that the last game didnt have bullet wounds and knife marks on an enemy. An extra bonus if the game had a house of the dead style gore system where you blow holes and gashes anywhere on the enemy's body.
animations: Lets face it, the worst part about fallout 3 was the animations. They were robotic and stiff. This time around they need to be smooth and fluid. If you shoot someone in the head, they should react and not stand there like a stiff. They should hold on the wound or die.
navigation: The fast travel was excellent and I got to all my mission's with ease. But if the menu was more legible and a short tutorial was provided it would have been even better. I know there will be vehicles in vegas, so I wont even mention it. Lets hope a vehicle will crush enemies and turn them into mesh when you hit them at 60 miles per hr. It would be nice to see a carmageddon style carnage system.
design flaws: Fallout 3 had repeated level designs for sewers and underground caverns. If you are going to repeat them you might as weel remove them entirely.
load screens: Would be great if the game only loaded when the game started up.
multiplayer: I dont care what they do, co-op death match. Fallout just needs a 2nd player or more. on and offline please.
ammo: Please allow the player to carry a lot more ammo than before.
camera control: Please dont make 3rd person mode ugly. Treat it like a normal 3rd person game. Maybe enable a cover system.
Realism: if the game is an rpg make the towns more realistic. Like have activitys. When you buy things or interact with your hands, show the in game players hands. Show them picking up objects and taking it to the counter. Thought breakdown did a good job of showing off the characters body and interacting in an intimate way.
Well thats all my concerns. I could go on and on, but those are the main problems with the last game.