Oh really? I always play on very hard and hardcoe, still I have only done the main quest with one of the characters (Out of 3).
And why should an open world be an excuse for a bad main plot? I think FONV delivered an open world (if not as big as FO3:s) and a good main plot.
I also find that FONV has more logical "pauses" in the main quest as opposed to FO3:s which feels alot like a railroad.
I also didn't like the "pauses" in the main quest in Oblivion. I mean, you could adventure and sidetrack as much as you like, but from the beginning there was some sense of urgency. If you like to stay in-character, you can't really adventure for 6 months and then suddenly remember, "Oh yeah, there was this whole thing about the Emperor and the Amulet, I forgot, silly me..."
I actually preferred Morrowind... from the beginning, you'd report to Caius Cosades, and the first thing he'd told you was, go out, get some experience, join a few guilds, make some money, buy some armour, and come back. It came much more natural to go out adventuring, in that context.