1 - Of course everyone wants more customization for their characters...
Skin Tone, Hair Styles, Accessories, etc
2 - Like in Hellgate, I would like to see Dye Kits, allowing armor to be color schemed.
3 - Respecing is a must. Nothing stinks more than putting your skill points into random skills you decide not to use later or when you would like to max out a particularly useful skill.
4 - The ability to forge weapons and armor. Similar to WoW professions but you could apply the stats for a new weapon onto the model of another, thereby keeping the cool looking sword or armor you have but upgraded it.
5 - A shared stash between your characters. Thereby disabling the need for Mule characters and enabling simple trading. A Mail system would be nice for trading between friend's characters as well.
6 - Disable the need for ammo count. Potions, arrows, bolts, etc. This would enable faster play without worrying about ammo count.
7 - Make certain legendary items drop from bosses that would make sense, rather than anything could drop anywhere. I remember finding Griswold's Edge from a barrel cluster in Hell. Why? I would like drops to make sense. They can still be rarely dropped but specific drops from particular enemies would be appretiated. Ex: Izual should drop Azure Wrath.
8 - This may already be implemented but just in case. The character creation screen where each class is standing around a fire and walks forward once selected is how I would like the character selection screen to be for characters that have already been started. For D2 the characters are there in their gear at the Main Menu so why not show the new models in their gear on the landscape?
9 - Some more exotic weapons would be great. I've seen that someone posted Whips, which would be cool. More diverse Katars than simple claw and spike designs (Think Bloodrayne katars), whip-swords, bone weapons, bladed disks, matchlock rifles/pistols, living weapons, and even demonic weapons would be great.
10 - More specific magic find. If you could attune this to different pieces you are looking for, it would be way more useful. Rings, armor, helms, swords, etc
11 - The green armor/weapon sets would be interesting if they displayed more aura/particle effects depending on how many pieces of the set you have. Ex: One set is more demonically themed and makes the characters eyes glow red and the character's body pulse with black energy. With each new piece the eyes and black energy become more vibrant.
12 - For Multiplayer PVP purposes, both players have to agree to be hostile, while in town, to be able to attack one another. Rather than one player flagging hostile and relentlessly attacking others or attacking during a boss fight. Mutually agreed upon hostility is a good thing.
13 - Along with more diverse weapons, motions and attacks with certain weapons are different. One does not use a katana like a broadsword or visa versa, so each weapon type should have its own attack style.
14 - Customized taunts would be neat. Say a specific emote could be attached to text and/or audio. Though of course people could take this a bit far.
15 - Everyone loves the secret cow level. So whatever is done with it, or something similar, make it repeatable. Some difficulty in discovering it and the requirements is fine, just allow it to be visited repeatedly.
Okay. Enjoy all.