Skyrim sold something like seven million copies, and plenty of those sales were from "casual" gamers. These are the gamers that are used to six hour campaigns that funnel you from corridor to corridor killing hordes of enemies. Most of my friends are "casual" gamers. I remember back when Oblivion released, the consensus among my friends was that Oblivion was fun, but most of them gave up after ten or so hours because they couldn't figure out how to beat it and got overwhelmed by the choices and possibilities the game presented. They also thought that the combat wasn't that great, and that alone ruined the game for most of them.
Now Skyrim has released, and a few of my friends got the game. I've been hearing the same things they said about Oblivion: the game is too overwhelming, and the combat svcks. I really think that the Elder Scrolls series is going to be further "streamlined" in subsequent entries. I wouldn't be surprised if Bethesda were to entirely drop the Gamebryo engine and use a more advanced engine like id Tech 5. I wouldn't be surprised if Bethesda were to focus less on the RPG elements of the game and more on the combat mechanics. The actions gamers of this generation think that a town with only twenty unique inhabitants is stupid: they'd rather see a larger city, even if most of the inhabitants are generic filler NPCs.
If Bethesda is really going to appeal to the mainstream gamer, I would imagine the series becoming something like Assassin's Creed, but with a customizable character and loot drops. To be honest, I wouldn't mind a game like that set in the Elder Scrolls world. I just wish Bethesda would make up their damned minds about what they want to do with the series. As it stands, Skyrim is a game that will disappoint both hardcoe RPGers and casual gamers. RPGers will be disappointed because the game has shallow RPG elements and lackluster character development. Casual gamers will be disappointed by the subpar combat and animation, and will likely be overwhelmed by the size of the game.
I'm definitely curious as to what The Elder Scrolls VI will turn out like. Maybe Bethesda will reinvent the series like other developers are doing, and just call it "The Elder Scrolls". Anything can happen.