They've stated that they want the game to have a Bioschock type feel to the game progression. RPG elements are not going to be a big part of gameplay, but there are a few types that we know of so far, such as building your vehicles and doing missions to get money to upgrade your equipement and such. I'd say if you have played Far Cry 2, it will have as much RPG elements as that, plus a few surprises. My main concern would be if it warrants much time investment. Like someone said above, if its only worth one playthrougfh, it wont be worth it. The gameplay does look solid, but with a lack of "true" detials, I'm not completley sold on this game. Even Fallout NV was worth multiple playthroughs, so I really hope id knows what they are doing.
If this so called "gargantuan" world is simply the level of Borderlands empty plains, then I want no part of it...And I loved Borderlands for the record.