Lemme preface this entire post - I played XI for about 4 years with a controller/keyboard, so I know that a lot of the deficiency in XIV's interface stems from a legacy of "PS2 limitations", etc. We're past that now, so I'd like to identify a lot of areas for improvement.
I'm sure a bunch of this has been covered by other people, but it merits saying anyway.
Movement control inconsistency
In WOW, I have strafe set to A/D, and turn to W/E. When I'm on autorun, I have a lot of flexibility in movement without breaking autorun. In XIV, I tried to mimic this, but they both turn on autorun, and both strafe when not on autorun. The only time they function differently from each other is in first-person perspective.
Camera controls
LOTRO and WOW have a snap-back camera you can use by left-clicking the screen and dragging the mouse around. That'd be nice to have to look at scenery as you run past.
Also, can the maximum angle for the camera be increased? I was kinda disappointed that I wasn't able to get a really good view into the chasm in Coerthas while crossing the bridge.
Keyboard mapping options
The keyboard mapping needs to support more keys/buttons in the interface. I was pretty shocked that I couldn't use Mouse3/Mouse4/Mouse5. I usually use Mouse5 to autorun in WOW, and it'd be nice if I could map those controls. Also, some keyboards have F13-F15 all the way up through F20, but the XIV client says they're not allowed for use. Others have custom keybindings. I don't own a Nostromo N50 or a Logitech G13, but I'm pretty sure some of them incorporate unique key names without needing a UI to map them to normal keyboard letters. DirectInput should allow for this.
I was surprised to see what made the cut for the mapping list and what did not. We have presets available for synthesis, for browsing bazaars, for checking players...but not for Teleport? What about assigning mob markers? It'd be great to be able to toggle that with a hotkey. It would also be good if we had more keymappings for manual target selection. We already have Tab/Shift+Tab for left/right, but if we could have hotkeys for next/last Enemy, next/last Friendly, next/last Party Member, next/last Attacker (since this targeting mode is being added soon).
Menu simplifications/consolidations
Every time my NPC linkpearl comes on, I always have an impulse to click it. It'd be nice if that could be effected. It would eliminate the need to open the menu and then open the NPC Linkshell entry and then select the specific pearl. Three clicks down to one.
Similarly, when being teleported, why not just add two interactions, and short-hand the interactions to "Accept Teleport: Location" and "Decline Teleport: Location" without confirmations? Similarly, a lot of other interactions, like opening the Aetheryte menu, could shorthand without needing us to open the main menu. The options should still be there, surely, but if I have a mouse, I should be able to just click the icon.
It'd also be good if I could change targeting selections with the mouse by clicking the mode indicator. I don't use a controller and I still can't figure out how to change target modes in /targetmode a.
Social Lists doesn't need the intermediate window for Friend/Blacklist. Just a single window with tabs. Also the Party window functions Recruit and Search could be moved into the Party Details window, and just skip the initial window.
Return could be moved into Teleport. It's a teleport action, and frees up some space in the Main Menu area which can be used for more important tasks.
Point Allotment (assuming it stays in the game in some fashion after the removal of physical levels) could be incorporated into the General Attributes tab of the Attributes window. Similarly, it frees up space in the main menu. And on that note, why aren't Key Items in Inventory?
Onscreen indicators
In the vein of the update notes mentioning a threat indicator showing relative enmity levels, it would be nice if players could toggle additional small widgets to show the number of items in the pack (ammo counter) and the current status of AOE, toggled or not. The AOE indicator will help players to know what the current setting is without having to target a cast.
We also need some way to know how far we are from targets. If not a specific distance measurement, which would be nice, at least a way to know which actions can be completed at a given range. In LOTRO, the unusable actions are greyed out/disabled, and in WOW the hotkey numbers show as either grey or red based on the validity and range of the target.
Screen widgets
It's great that most of the interface can be moved around. It would be good if there was a configuration option that allows the interface to be "locked" so that players can't accidentally move things while mousing. Further, I'm constantly trying to select things through the status icon indicator, and it'd be good if we could enable/disable the toggling of the status icons as a selectable area.
In both WOW and LOTRO, the mousewheel can be used in a context-sensitive manner to scroll the chat windows. If the mouse is over a chat window, the wheel automatically scrolls the chat.
Crafting status indicators
If I am under the effect of, say, Preserve, show it in the status icons. It's relevant, and that way if I'm blindly crafting while surfing the web, I'll know if I should toggle an ability if it comes up (so that I don't overwrite one already up).
Crafting command window resizing
When an extra crafting command becomes available, the command list gets a scroll bar. It's already pretty small, so rather than adding a scroll bar, make the window dynamic-height vertically, or resize it so that the addition of commands doesn't make the list scrollable. For one thing, sometimes when I use an ability, the list does not always reset to the correct initial position, especially if I have multiple abilities available, so I might accidentally select Rapid when I intend to select Standard.
There's a lot of wasted space above the progress bar, there could be dedicated slots there for abilities, and then they would individually light up when they become available.
Red/Green colorblindness
The colored dots for mobs and NPCs on the minimap aren't easily distinguished by people afflicted with R/G colorblindness, especially with the background color they're rendered against.
This also translates to the Gear window when changing gear - it's difficult to see whether a number is going up or down based on the color alone. I would suggest using blue for positive changes and red for negative ones.
Current Target
The "current target" indicator should be clickable as a targeting selection. If I already have a monster selected, and I cast a spell, the targeting cursor should automatically go to that mob so I can just hit Enter. I acknowledge that it may be the intended behavior and currently when it doesn't work that way it might just be a bug. In any case, I should be able to just click the name of the current target just like I can with the party member list.
There's also a bug that's been creeping up a lot lately for me when I'm target-locked on a corpse after a fight is over when I never locked on that target to begin with. It makes pursuit leves rather annoying because when my character doesn't move right away, I don't know if I'm afflicted with Bind/Sleep and I just haven't noticed, etc.
Character Status Animations
When I get slept or bound, I see the status icons, but if I'm busy juggling healing/nuking tasks, I may not notice right away, and the status log messages are not consistent. In addition to a prominent "Command failed for reason XYZ" error on-screen, it would be helpful if the player-characters could animate in such a way as to show visible status ailments. If they're asleep, they should be kinda slouched and have some animated z's bubbling up from their heads, or the classic Japanese snot bubbles. If they're bound, show some arcane energy extending from the ground wrapping around their feet. If they're slowed, render the battle animations at a slower speed, and if hasted, faster. I think the idea is clear.
One last note - macros
Everyone else already knows this I'm sure, but the text in "/? equip" is wrong - "off" doesn't work, it's "sub" just like it was in FFXI. Also, why are these slot names case-sensitive? It'd be good if they didn't have to be.