1. Update the UI!
Clear out the clutter & make it more aesthetically pleasing by implementing a minimalist approach and a color motif, preferably black and opaque. Small bits of color are cool for skills and such, but nobody likes a mess of colors on the screen.
-Example: Elder Scrolls Online

2. Update character models!
Do I really need to elaborate on this?
-Example: Every new MMO released in the past few years

3. Re-do the way skills are used.
There are way too many skills for pretty much every class in the game. Take a tip from Guild Wars 2 and make it so you can only have 6-8 skills slotted at a time.
-Example: Guild Wars 2, Elder Scrolls Online, The Secret World

4. Implement an achievement system!
I realize we already have deeds and such, but they're not quite the same. I would prefer to have something more akin to SWTOR & ESO, with a series of possible achievements listed before hand with an appropriate award system attached. This extends the longevity of the game in numerous ways.
-Example: Elder Scrolls Online, Star Wars: The Old Republic

5. Improve the legendary item system!
It's a grind and always has been for the most part. I thought it was pretty awesome when Moria first came out, but since then it's been nothing but a hassle every time another expansion releases. Rather I would prefer we move to a system where your weapon is maintained and improved on, but ultimately remains the same weapon throughout your adventures, kind of like how Orange weapons can be upgraded in SWTOR.
-Example: Star Wars: The Old Republic's weapon upgrade feature