The Character Window

The completely redesigned window contains two panes, one for your character and gear and the other a collapsible window with all your character stats. If you feel that a certain category (e.g. "Melee" or "Defense") doesn't concern you, rest assured because all of the categories are also collapsible. You will also notice the skills tab is completely gone, with that information being moved to other pages. The rest of the tabs remain unchanged.

Leveling Up

One of the really major changes to the User Interface is the addition of a set of notifications when you level. You get a message telling you what level you are, what new skills are available to be trained, a notification that you've gained a talent point (if you have), and what new features are being unlocked at this level. The features currently in the list are: Battlegrounds (10), Dungeon Finder (15), Apprentice Riding (20), Expert Riding (40), and Artisan Riding (70?).

A level up notification pop-up can be reopened at any time by clicking the level in your chat window message.

Spellbook

The spellbook has also got a nice makeover. Besides now only having one rank of each spell/ability, it also displays at which levels your future abilities can be learned. And it looks prettier :)

Professions Window

Professions are no longer listed under your general tab in the spellbook but have moved to their own tab inside of the spellbook. Inside you will find all your professions, with progress bars for the skill level and any specializations if you have one. Each profession will have all of its relevant spells linked to it (e.g. Jewelcrafting will have Jewelcrafting andProspecting

).

Tradeskills

The Tradeskill window has also received a lot of loving with this expansion. Besides things being moved around to make more "sense", a few extra filters have been added—such as the "has skill up" filter which obviously shows you all your craftables with skill ups!

Trainer Window

Another revamped window, staying in theme with all of the other changes, is the Trainer Window. Now that there's only one rank for all the abilities, this was a much needed change. The changes here are mostly visual.

PvP Window

The changes to honor and arena points, along with the new battlegrounds made way for some rather sexy changes to the PvP window. With separate tabs showing all your battleground and arena team info, it will be your one stop shop for all your PvP needs.

Minimap

The minimap has also received a few changes, the first of which is the ability to track multiple items! No longer shall you have to decide between looking for fish or finding that elusive Frost Lotus. The other is an addition anyone who has ever used QuestHelper will enjoy: there is now a minimap arrow that will direct you torwards the next objective if you use the ingame quest objectives.

Source: wowhead.com