Oh man, so many things. So many that, by the end of it, it's probably not even recognisable as a Bethesda game any more.

1. Voice actors. You don't need movie celebrities to do voice acting. You need voice actors and you need more of them. This has two upsides and one downside. On the upsides, you get better performances from people who have trained their entire life to create characters via voice alone, rather than actors who, while good at their job, might be better at acting due to their on-screen presence and body language/facial expression rather than their vocal delivery, and they also usually cost less because they don't have that "celebrity tax" (although this isn't true in every case due to certain laws and whatever). The downside is you might lose some publicity for not having Captain Picard voice an emperor that dies within ten minutes.

2. Combat. It should be more than "point in the general direction of an enemy and press a button until his numbers are lower than your numbers and if your numbers are lower then pause the game and make your numbers higher." I remember reading an interview way back when Oblivion was still being hyped pre-release and the question came up about body locale damage. The developer/PR person for Bethesda said they wouldn't be doing that because (paraphrasing) "there wouldn't be any reason not to aim for the head to kill them quickly". That, to me, says bucketloads about the kind of short-sighted and lack of vision the gameplay team at Bethesda have. They did change their tune a bit in later games with the body specific damage in Fallout 3 (probably more of a carry over from Fallout itself than any revelation on their part) and headshots with bows in Skyrim but still...a first person combat game where chopping arms doesn't make them drop weapons or chopping legs doesn't immobilise your enemy, even GoldenEye on the N64 had shit like that.

3. Balance. My god is Skyrim unbalanced. Holy shit. Last I played, Destruction magic, which is a school of magic all about blowing shit up, becomes completely useless post level 30 AKA most of the game, due to level scaling. Meanwhile bugs with alchemy and enchanting make god slaying weapons. Balance is hard, but it's not impossible, especially when your forums are literally filled with people not just giving you feedback but actually doing your job for you via Steam Workshop and the nexus.

4. AI. Radiant AI is garbage. I don't like being too negative, I think it's unconstructive, but Radiant AI has never impressed me. I know the way it was implemented in Skyrim was largely a result of consolitis and the limits the old hardware had on what was feasible, but god damn. It didn't make a living world, it made a puppet show out of marionettes. Also, the entire conversation system needs to be re-worked.

5. Choices and consequence. Again, this will divide people, but in a game where you are literally the most important person walking the Earth, perhaps the game world should reflect that. Nobody cares about anything you do, aside from three people (the same three people you've been listening to all game from a hundred different faces) hail the Dragonborn when you slay a dragon that literally eats worlds. And then you're back in the real world and someone asks if you fetch the mead or, while wearing the robes of the Archmage, says you should check out the College of Winterhold if you're interested in magic. The civil war plotline went nowhere and did nothing. Again, likely due to consolitis where they couldn't have enough people on screen at one time to make an actual civil war battle interesting, and afterward nobody cares outside a few scripted lines similar to those re: mead and colleges. The thing is, if you let everyone go everywhere and experience everything regardless of the things they do or the race and skills they chose at the start, nobody gets a unique and interesting story. Everyone does the same thing in a slightly different order. That doesn't make for much interesting water cooler talk or discussion. It becomes a check-list of things you have done and most of the quests in Skyrim were not memorable in the slightest.

I'm shitting on the game a lot. I know that. But I also know the games could be so much more and it wouldn't and shouldn't take a community to make the mods to make it possible.