Over the months I've been playing, I've seen both the good and the negative sides of the UI. I like how the HUD is minimalistic, and wouldn't change that at all. But why are the UI setup on bring-up menus so blotched and illogical?
Guild store UI: Really needs an upgrade. No search option is the biggest disadvantage of this UI. A lot of people use it, but a lot of people won't bother even trying. It needs a search option most of all, but it also needs work on how it lists items.
Character stats: This really is the biggest scrambled mess I've seen in some time. First of, the tool-tip isn't accurate at all. Spell-power per example states it increases your spell's damage and healing, but if you're a sorcerer, you don't need spell-power but weapon damage to increase your healing spells. There really aren't that much logic in the stats and it's not apparent from the stat UI what does what and what affects what.
Buff interface: This is something that needs to be added. Both for targets and player. I know that you have visual queues on your character on what buffs you have up, but in the heat of things, I really don't have time to stop and contemplate whether or not my character's hands are glowing or not. A simple UI build into the UI to monitor what effects are on you, and a simple way of telling what effects are on your target, as well as if you have debuffs or not.
Inventory UI: This is actually not that bad, it's a list and it's easy to sort through weapons and armour. What I would love however is a simple "check" button at top that says "mark as junk" and allow you to simply check this one and click on the items you want to send to your junk inventory. A lot of times I pick up weapons and armour items because they sell for some good gold (around 2k per sell), but sorting through what to keep for research and what to throw away, is at times irritating. Right click, mark as junk. So a simple check box to make life easier.
Grouping UI: Multiple dungeon selections. Simple, have a check-box and make you simply check of which dungeons you want to group for. Same goes for everything you have multiple choices for. Want to do several things in the world? Check-boxes. Want to select more dungeons to queue for? Check-boxes. As it is now, you can only select 1. This is something that needs to change as it works against the grouping UI.