If we are talking about the last decade in gaming and rpgs. The big games have been more like fps-games in rpg-drag. The only recent game i can remember (that wasn't that) is basically Dragon Age Origins (which i liked).
So i want that experience again. The top down thing that they are doing. Beyond that i think that a good story that makes me want to play "just another hour" is important. The atmosphere in the world-building is also important. A good example of that is that game Stasis (check out the alpha-demo if you haven't already). That game oozes atmosphere.
But this was about the one thing i would want in the game. So i guess i would go with atmosphere. I think the the rest i mentioned just feeds into that anyway.