I dunno what engine it will be using, but there is a Fallout MMO in the making supposedly, though theyre discussing some deadline shit with Bethesda Softworks atm, as they own the fallout merchandise of the now.
One thing i fucking HATED from Oblivion was the enemys leveling thing, in Fallout 3 too. It was way worse in oblivion though, no matter where you went the enemies were always leveled with you. if you got mauled by a troll at level 1 you couildnt train till level 10 and go back and kick its ass, it was level 20 by then and you'd get your ass kicked all over again. Either that, or it was piece of cake all the way through.
and one other thing i fucking hated, the compass system, took every bit of fun out of exploring and reading the map and directions, no matter what, there was always the arrow pointing at shit. Killed a lot of hte fun of both games(Oblivion and F3) to me.
And on the Fallout note, cant fucking wait for Fallout: New Vegas, as its being developed by the original developers of Fallout and Fallout 2, praying for more dialogue and more coherency, and less bullshit