The old UI looked way better. It had a style which was nice and minimalist, but also functional. The current UI has no coherent or congruent art direction and looks severely dated. It honestly boggles my mind why they changed it from a modern, functional, good UI to a dated-looking, less functional one. The shiny, beveled button look is so 2000. Many big software companies have moved to the flat-UI, material design. E.g. ios, android, windows 8; so it's funny that spiral knights has gone the opposite way.

To qualify what I said about the new UI being 'less functional':
- That huge face icon that shows a picture of the knight and the sprite. This one is by far the worst addition. It takes up a lot of the screen especially on smaller resolutions and is completely pointless. (not to mention ugly)
- The health and shield bar that takes up tonnes of room (showing health and shield percentage is brilliant though).
- The cluttered footer bar. I prefer the vials up top like how they were before. This isn't a big deal though.
- SO MANY MENUS - you have four buttons on the bottom right, five on the bottom left, and another set of buttons on the right. Plus in missions you get a little objective menu too. To make it worse, EACH SET IS HIDDEN USING SEPARATE BUTTONS. This is just terrible UI design, especially compared to the old one which gave you way more screen space.
- The forge menu is also just terrible and has that animation that takes all of three precious seconds when you forge.

A good UI can be classified by displaying essential information and giving the player access to the essential menus in a clean, concise UI that doesn't take over too much of the screen. Many of the buttons could be aggregated into one button, and some could be left out entirely. Additionally, a lot of the icons have all these extra decorative bits and are too large, taking up extra space. The big face in the top right is completely useless.

I'm sure many people will disagree with me and will say they like the new UI better, which is fine. Agree to disagree. This is why there should just be an option to change the UI style. Easy to implement, and keeps everyone happy.