I'd add a few more options when it came to the factions. It seems a bit weird to me that they included an option to go on a crusade against Dark Brotherhood but not for the Thieves Guild, I also think it's kinda fishy that you can literally become Thane for all of Skyrim, but you can't put yourself forward as a candidate for the throne or at least become a Jarl. I mean you could literally become the God of Madness last time around, but I can't even rule a poxy little hold like Morthal here?
Speaking of which, being Thane needs to have way more perks, yeah I get a decent weapon and the guards will excuse some of my bounties, but a little more then that would be nice.
Last of my big changes would be to make the Marriages a bit more complex. It really should take more then a simple little favor like finding them a book to make someone want to marry you. And once they do marry you it'd be nice if they could have more interactions then "Give me money," and "Cook me food" which really made me kind of uncomfortable after I thought about it for a bit.
I really don't need much, just a dialog option to say "I love you?" Maybe a hug button? A slight difference in their dialog to show some differences between them? Anything at all to make this feel like a loving relationship between two living beings?
I know that beyond the huge central characters Bethesda isn't the best with characterization but these are literally the characters you're supposed to grow the most attached to but they feel barely above every single other NPC in the game.
Aside from those it would really just be changing some little nitpicks I have like separating the pants and the shirts, adding back in Short Swords, and bringing back that Armorer skill (It just feels slightly, wrong to play Elder Scrolls without that tink tink tink sound every few minutes). I'd also go backwards a bit with the weapons skills, have axes, blunt weapons and blades separate skills, with one-handed/two-handed perks for each staying within their specific skill trees.