It's a brand new game as far as I know. Looks like fun, I really liked the first one, and by first one I mean third one. Even though it's really the first one. Sort of.
I thought it was new, but some of what I read made it seem like it was just a FO3 DLC. Sounds like big improvements include: - Weapons can be repaired to max and the repair skill is used for crafting or making them better - You can make more weapons and can now make poisons. - You can pick a trait at birth. One example was you gain a bonus to perception when wearing glasses but lose something if you are not wearing glasses. I don't have the source at this time because I read it last week.
They've also added Melee 'special moves' extra stuff for the VATS system for melee. Which is good for me because i spent most of the lower levels wandering around with a power fist Level and stat progression is supposed to be different too. The timeline is set after the events of Fallout 3, but on the other side of the continent.
I will probably get the game but not until its been out for a while I think. Still playing Fallout 3 and cant see me getting board or finishing this for quite some time.
I loved FO3. I am alittle sad I was burnt out before the Botherhood of Steele expansion (or which ever expanded the story). It's one of those games I think I'll go back to at some point but haven't.