Well for starters I would've had the world be more reactive to your progress through it. So much of the game feels limp because major events that should realistically impact the world kind of don't. The Civil War aspect is terrible because it's basically another guild quest chain like the Thieves Guild or something. The inconsequential dialog is far too static and based solely on which tree you have the most shit in rather than, say, the fact that you're kind of a big deal. More diverse quests would have also been welcome. When the game was in development a great deal was said about the dynamic, radiant quests but in actuality it's just an endless series of fetch quests that get foldered into the miscellaneous tab or else it's diving into another prefab cave to kill like six bandits. 

The strong part of Skyrim, which is the strong part of any given Bethesda game, is the big dumb world. Bethesda knows how to make a world that rewards exploration (the quality of the world is debatable but ehhh) but they utterly fail at giving a reason to stick with it long term. The various guild quests are poor because you do like five things and suddenly you're the hotshit leader after an hour. It's so wrapped up in being a power fantasy that it ultimately makes the power fantasy part less interesting because, again, the world is so god damn static. 

The questlines WERE dull, particularly the side quests. I can't speak to the main quests because every time I play Skyrim I wind up installing mods for like five hours then I start a game and get bored right around the time you fight the first dragon and I'm done after like an hour and a half. But side quests boiled down to talk to person A, go to place, kill x or find y or kill x AND find y then report back to person A for a leveled reward. In a game that takes pride in letting you "do what you want" the things you wind up doing are remarkably similar. 

How would I have made Skyrim better?


By making it a good game.