No idea if anyone adressed something like this here already, but based on my experiences in Morrowind, Oblivion and Skyrim here are a few things I'd LOVE to see (again) in TES VI.
1) More diverse wearable equipment again:
Not counting weapons and shields you can wear 8 items at once in Oblivion (boots, greaves, cuirass, helmet, gloves, 2 rings, amulet), 7 items at once in Skyrim (boots, torso armor, gloves, helmet, 2 rings, amulet) and 15 in Morrowind (boots, trousers, greaves, shirt, belt, cuirass, left shoulderpiece, right shoulderpiece, left glove/vambrace, right glove/vembrace, helmet, 2 rings, amulet, robe)!
Morrowind actually allows you to customize your look! You want to play as a mage but also want to look like one, even though you're wearing armor? - wear a robe over it! Wanna look like a gladiator with armor only on one arm? - no problem! You think it makes no sense to only wear your underwear under your armor? - You're totally right! Wear normal clothing underneath (you can even enchant it )!
2) Recharging enchantments:
So, in Oblivion and Skyrim you pick up an enchanted weapon sooner or later. Well, that's great, I guess, but once its charges are used up you have to use a soul gem to recharge it. Did anyone of you actually ever bother still doing that after a few times?
In Morrowind items recharge themselves over time which I think is much better in terms of gameplay.
3) Your abilities matter:
You are Shadrub gro-Agbaz, an orc berserker who has killed hundreds with his bare hands and even more with his battleaxe Bloodthunder all the bandits, necromancers and draugr of Skyrim are cowering in fear when they hear your name. As you stand over the headless corpse of the high elf Ancano in the Winterhold mage's collage, blood dripping from Bloodthunder's blade, Tolfdir approaches you. He's all like "Wow, great job! You know, since our arch mage is dead, we need a new one. Since you've cast an entirety of two spells in your whole life, all your magic skills are between lvel 5 and 10 and you knew how to hold the Staff of Magnus the right way around that totally qualifies you for the job! Congratulations!"
In Morrowind this is much better managed. To actually rise in rank in a faction you not only have to do the quests, but also have to level certain skills. Every faction has like 6 skills that matter and for example to rise to a certain rank you are required to have one of these abilities on level 50 and two on level 20. So getting to the lead position in one of the guilds in Morrowind actually feels like you deserve it, because you've worked for it.
4) More different weapons
Daggers, swords, maces, axes, greatswords, warhammers, battle axes and bows. That's basically all the variation you get in Oblivion and Skyrim in terms of weaponry. Ok, there're also crossbows in Skyrim again if you own the Dawnguard DLC, but compared to Morrowind that still is a little meager. In Morrowind you have: daggers, tantos, wakizashis, shortswords, longswords, cutlasses, katanas, greatswords, dai-katanas, one handed axes, twohanded axes, maces, warhammers, spears, halberds, battle staffs, bows, crossbows, throwing darts and shurikens. Now, you might argue that the Akaviri katanas in Oblivion and Skyrim basically are katanas, too, but in those games they nonetheless are simple swords considering how they're used. In Morrowind, though, every type of weapon has slight differences...
5) It matters how you use your weapon/you are able to do different attacks
Basically all you can do with a melee weapon in Oblivion and Skyrim is swinging it around. In Morrowind you actually had three different attacks: stab, swing and cut. And that wasn't just for the look. Depending on which type of weapon you used one attack type might be way stronger than another one. With a katana for example you could deliver powerful cuts and decent swings, but only rather ineffective stabs. A spear on the other hand was only really good at stabbing, but due to its reach you could also hit enemies with it while they couldn't hit you.
6) NPCs can give you extended information
In Oblivion you could still at least talk to pretty much every NPC and ask for rumors. In Skyrim you can't even talk to a big part of the NPCs. An example: In Morrowind every random guard could not only tell you the newest rumors, but also about the place, the surroundings, important people, give you tips for adventuring, give you sometimes detailed information for how to best get to a certain place like another city, etc. In Oblivion the town guards could at least give you directions most of the time. In Skyrim the guards won't talk to you properly anymore - exept if you've committed a crime. Sure, you can randomly get the newest rumors from them, but most of the time they'll just tell you about "how they once were an andventurer, too"...
Ok, all that information from NPCs in Morrowind probably was mostly possible only due to the fact that you had to read the dialogue since the characters had no voice cover beyond basic interaction lines. At first I actually thought that would quickly ruin a game a bit for me - reading extensive dialogue to get information instead of listening to it? But you know what? I sometimes spent half an hour talking to one NPC, because the dialogue about pretty much everything explained the game mechanics to me - and it worked! I didn't feel like I was in a tutorial and wasn't bored by a seemingly endless dialogue but rather felt myself getting immersed in the world in a nice way.
7) Popularity and haggling
People who like you might give you different information or any information in the first place. People who don't like you might refuse to answer your questions or to trade with you. In Morrowind and Oblivion you could see how much people liked you and if they didn't want to spit out their information you could try to persuade them (although I never really figured out how that works in Oblivion...) or bribe them. Why was this lacking in Skyrim??? Ok, there were a few cases where you could actually persuade/bribe someone, but those were all scripted. You couldn't go up to a merchant, persuade him to like you and then get better prices from him.
Oh yeah, speaking of merchants - it's actually a nice thing to haggle over prices in Morrowind and it's really simple, too. You'd give me only 589 drakes for all that stuff, merchant? Give me 600! - and as long as you keep it reasonable and/or the merchant likes you it works. I actually can't remember if you can haggle in Oblivion, but in Skyrim it's definitely missing.
Those are just two little things that make a game feel more complete.
Might continue with this somewhen... there's a lot more.