This game’s UI was good for 2010, and it's okay now. But there’s a lot of improvements that can be made. Personally, I’d like to see a complete overhaul of the UI, but instead I’ll be giving suggestions on how to at least improve the current UI.
Bazaar: The bazaar definitely needs user interface improvements. Firstly, there are 47 pages of items in the decorations category. Now I’m not complaining about how many decoration items there are, because the more the better, but the way of clicking on each name downward until you get to the end of the page, and then clicking next so that you can go all the way to the top is not fun. Again I think this needs a complete overhaul but instead I’ll suggest a more likely and easier way to massively improve this. There should be an arrow key to go down and up at the bottom of the page, next to the “previous page” and “next page” arrow keys. When you press the down key, you go down by one item, and so on. This means that you don’t have to constantly move the mouse a centimeter down every time you want to see the next item. It sounds like a small thing, but it would greatly improve the experience. I find myself clicking on the next page button continuously, only looking at the first thing on that page. Adding a down arrow would solve that. If you're unsure about this being an issue, trying going through all the decoration items as if you were a casual player, you'll definitely feel it in your wrist. Something even better would be to make it so your keyboard arrows work with the bazaar. So your left and right keyboard arrow keys switch pages and the up and down keyboard arrow keys goes to the item above or below the one that's selected. Also, please add a search bar to the bazaar that can either search the entire category or the entire Bazaar. The crowns shop is a great example of the type of UI the bazaar needs. Images of the items so you don't need to click on each one, and a search bar that can either search a category or the entire shop. This is exactly what the bazaar needs.
Search bars: Please add search bars on everything. The bazaar, your backpack, your bank, your crafting tab, your housing tab, everywhere!
Crafting: Please add a castle block category to the crafting tab in the spell book. Right now, all of the castle blocks are in the outside category and clutter the category. It’s also inconsistent because there’s a castle blocks category in the housing interface but not in the crafting tab. It would also be nice to unlearn certain recipes that are there only to clutter your tab, or maybe hide them.
Backpack: In the same way that you can move up and move down the position of your gear sets, it would also be cool to have the ability to move your normal gear up or down. Alphabetical organization is cool as a default, but it would be nice to have your own organization too. Being able to place your most used mount or wand at the top of the page would be very convenient. And to have a search bar for people who have like 5 pages of mounts would also be nice.
Bank: Same concept as the Bazaar. Down arrows and a search bar.
Housing tab: Ability to change the order of items in your housing tab like you can in gear sets.
Friendslist: I have no complaints about the friends list because the UI was revamped and it's very good. One thing though, is that it's missing the black gems and stars. There are six stars, purple for storm, blue for ice, green for life, yellow for myth, orange for balance and red for fire. Where’s black for death? If I like a friend enough to give them a symbol, I mostly choose these symbols and base it on their school. So for a death wizard I just have to give them the balance jewel cause there's no black jewel.