I miss weapons being unique and varying. Being able to loot a dagger and seeing it increase agility by 20 and also has a chance of procing a frost spell attack that hit's for 50 frost damage. Picking up boots that increase stealth's effectiveness by 5 levels and agility plus hit by 20 points. Or a necklace that inflicts 200 damage if the wearer is hit and increases intellect by 90. Can't forget about weapon oils either. Just fun stuff like that. Now its all just primary stats and secondary stats that are increased. Nothing else. It's simply boring now.
I miss procs in general. Even with talents. Passive procs. Out of know where bust out amazing burst damage.
Leveling rewards. Every level gained you something... Either a new talent or ability. Now you can go a level or two and not get a single thing.. It's just another level. Now with the talks of planned service to pay for instant level 90 alts just makes leveling completely unfulfilling.
Traveling. You had to travel everywhere. New level? New ability. Have to take a break and travel back to a capital city and see a trainer. Want to que for a battleground? Have to go see a battleground master. Que for arena? Same thing. Yes, its nice to be able to que from anywhere... But I wish they would make it that you can actually leave a city to do stuff... And not just sit in a city and teleport everywhere.
Unique classes and specs. I see a lot of people bringing this up and honestly it's something that needs to come back. I use to play a shaman and loved being the class that brought bloodlust. Then they gave it to mages... And oh do I miss the totem buffs... It was so awesome having a totem circle around you. I also played a paladin and loved being the class that brought the aura buffs. Now everyone and the kitchen sink has them. Keep class damage balanced and bring back unique classes and specs.
Class upkeep and maintenance. This ties in with uniqueness. Hunters needing arrows, mages needing dust and runes, paladins needing blessings, and rogues needing to buy their poison. This added a immersion factor to the game and made the class feel like the class. Hunters shoot bullets and arrows, and need a supply of them. Rogues need poison and need a variety of them. Mages are wizards and need dust and runes to cast certain spells. Now everything just magically appears, even for non magical classes like rogues and warriors.
Dark nights. How the hell did they screw that up?
Level appropriate guards for the zones. I miss level 40 zones having level 40 guards. Not somehow magically spawning level 90 elite guards. I don't even mean this from a gankers point of view. I mean this as flying my level 40 friend around and them getting killed by a level 90 elite guard that spawned over a level 30 city.
One cool thing that WoW really never had would be hybird enchants. They make some cool ones like increase damage to undead or elements, but they're worthless because thats all they do. It would be nice if they merge those in with worthwhile enchants. Like increase your agility or strength by 1500 and increase damage dealt to undead by 15%.