Grouping and PvE content in the form of instanced areas is, to put it lightly, pretty common in MMO's. PvP also seem centered around the same type of thinking, so called sandbox PvP. Having said that, I'm sure that Fallout Online want to be as much WoW-with-guns as Fallout 3 wanted to be Oblivion-with-guns. It will be fun and interesting to see what the good folks at gamesas will do with all of the industry standards.
Will there be a tank, healer, ranged and melee dps setup? In most MMO's there always seem to be a need for very defined classes in group play, and for solo play it's the always popular hybrid healer/dps class. Will there be a S.P.E.C.I.A.L version of speccing into a healer or tank or will everyone be able to be a (to use the MMO term) hybrid, with the ability to do damage, take a fair beating and heal themselfs?
Will there be instanced dungeons for groups, and how big groups are we talking about? Will there be scenarios/battlegrounds for PvP? It could get dangerously close to Team Fortress territory here; the sniper, heavy armoured minigun guy, stealth based guy etc. I know we probably wont see classes as we're used to, but to derive a bit from the S.P.E.C.I.A.L system of todays titles you can easily compare or translate it to a spec in most other MMO's.
There is a lot of things that will look a bit different from what most people are used to, i.e WoW and the WoW-like games like LOTRO and WAR. But how different will it be? Reinventing the wheel has proven precarious in the past with AoC for example.
Will there be TAB-targeting or cross hair targeting, will there be just the one attack button (fire weapon) or will there be some form of ability based combat that we haven't seen in the Fallout world so far? Simply taking what most Fallout games are about and translate it to an MMO is rather easy, but it will make little more then a co-op Fallout Tactics game, and honestly, who'd want that!?