The thing I have been missing the most is a better companion system. After playing Oblivion with Companion Vilja, I can't help but think Bethesda should have taken a lesson from this incredible player made jewel. For those unaware, Vilja is an incredibly detailed companion, scripted to react to the main quest, side quests, take you around for walks, she can adapt to your combat strategy, she can ride, drink, sleep, dress up on her own and she has literally thousands of lines of dialogue which allows her to feel incredibly alive. She has her own storyline, quests and personality you can develop, adding dozens of hours to your gameplay. There are also Morrowind equivalents, but I haven't touched Morrowind in ages to throw in examples. Here is her description, which proves how much a companion can do with enough development time: http://www.tesnexus.com/downloads/file.php?id=28977
Now imagine if Bethesda were to implement fully realized companions, using their talented voice actors, improving the AI and adding a companion wheel to help with interaction. While Skyrim's default companions are much better than Oblivion's, they are still inferior to New Vegas in both reliability and depth. Polishing companions may not be as enticing as entirely new areas to explore and adding new gear, but they sure add a new layer of realism and sympathy toward NPC characters. Companions done right can GREATLY enhance the way you interact with the gameworld and approach each quest.
DLC could include:
1) Companion wheel (fallout style) with more companion commands:
- Guard this area: Sets a patrol route around the perimeter
- Wait here: Adds AI packages to make them sleep, eat, sit and talk to nearby people (instead of just standing there)
- Stand by: To replace the current Wait.
- This is your home now: Make the location their new home.
- Please accept this gift: Makes them wear whatever you give them, regardless of attributes
- Hold your fire: Makes them passive until your first attack.
- Silence!/Speak up!: Makes humanoids and animals be quiet for awhile (annoying dogs!)
- Use melee/ranged weapons: Makes them favor a combat style.
- Assist me!: Makes them heal or use protection spells on you.
- Search the area: Makes them loot corpses and nearby containers.
- Be careful!: Companions go into stealth mode and won't set off traps.
- Ride with me!: Companions whistle for their horses and will mount and dismount when you do.
2) Improved AI pathfinding: Companions will always use the same door the player uses, will teleport if they get stuck on geometry.
3) Improved battle strategy: Companions will not charge if outnumbered, will attempt to flee if low on health, will take cover if using ranged attacks, will avoid enemies that can easily outmatch them, drink potions, use buffs more often and will always try to stay close to you instead of running ahead.
4) Hundreds of new lines for each companion: Companions will no longer repeat themselves over and over again. They will comment on both the main quest and major side quests as dozens of additional lines for different areas of the map, important buildings, points of interest. They will comment on your progress, battle prowess, screw ups, they will warn you against dangerous critters, hazards, traps. They comment on wild life, their backstory and other NPCS. They groundwork for this is already done, it's actual content that is missing.
5) Quests: Each companion now has an extensive backstory that will continue to develop in the course of the game, each major event triggered by how long they have been travelling with you. You get to know more about them, the longer they remain on your service.
6) Knocked out state: In addition to the kneeled state, in which they can get killed, now you can revive them shortly after they get knocked out. This should help with accidental deaths, but also gives you a chance to allow them to die, should you refuse to wake them up.
7) Crafting: Companions can be ordered to go out and collect raw materials and later they will proceed to craft useful items for you.
8) Romance: Romance with companions would be a chance for Bethesda to make amends for the extremely simplistic wedding system. Since they're more refined characters, additional lines and options would be available for each companion after you get to know and befriend them. No amulet needed.
9) Extended animal companions: Given the options to be played with, fetch items, and guard the area. More dog breeds, wolf companions and perhaps other sorts of animals.
10) Better environmental awareness: If told to wait in cities, companions will dress casually, will strip their armor and weapons to sleep, will sleep, drink and dance while resting in Inns, will shop for items they like if they have gold and will visit areas of interest nearby. Companions will engage in conversation with locals and attempt to improve their skills in training areas.
11) Companions improve their skills: Companions will not only level up, but will also attempt to learn new spells, new combat moves and actively search for new equipment if given the command to loot the area.