As previously predicted, the game will be based on a modified version of the Oblivion engine (which in turn is a customized version of the Gamebryo engine middleware). Fans of the series will be pleased to hear that they'll keep several parts of Fallout-series gameplay mechanics and even feature a battle system where you can pause time and spend action points on your moves.
But you'll be able to play the game in realtime for those who prefer that, and since the game is based on the Oblivion engine, I wouldn't be suprised if you can zoom into first-person. Bethesda said they would improve the third-person camera aswell, after recieving alot of negative feedback for it after Oblivion.
There target system will stay in tact from the franchise, with specific body parts that can be shot at and injure, and the same thing can happen to you aswell. There's going to be a karma system, and the game will feature between 9 to 12 different endings.
The health system will get a overhaul, and Bethesda will introduce a new system for radiation where you need to measure how much radiation it's in the water or other consumables. You'll also be able to sneak or talk your way through the game instead of just killing everything you see :)
Fallout 3 kicks off with your birth and your mother's death in a vault hospital. This is where you get to create you character as your father (voiced by Liam Neeson) hands you over to the DNA analyser, before removing his mask to reveal similar traits to the ones you picked.Massive Fallout 3 update
Emergent Game Technologies: Gamebryo
Fallout 3 gameplay details revealed