Only the absolute essentials, the bottom screen is clean, there is only one text label, everything is small but not unreadable, and the art is elegant and not distracting.
I took these yesterday, currently playing Avatar: Frontiers of Pandora and its kinda crazy how immersive the game can be when just exploring. If you ignore the top right (I had a resource pinned I was looking for) this is how the game looks when just traversing the world. Ubisoft knocked it out of the park with this aspect of the game (the character screen is their generic yucky paper doll interface though), and it runs at 60fps on a console to boot!
Warcraft 3 and Starcraft 1 had a really nice UI design, with it changing depending on the faction you are playing as. Something is really nice about animated portraits too. Especially ones for SC1. Heroes of Might and Magic 3 UI is also very nice. It's ornate, but also somehow not busy and shows you exactly what you need.
The HUD is the set of sprites layered over your FOV (field of view.)
The UI is how the controller maps to the gameplay, and the top tier one ever released, bar none, is in Robot Alchemic Drive.
The left stick controls your left arm, and the 2 left triggers control your left leg. This is mirrored on the right. Truly an amazing UI: easy to learn, difficult to master, and fun as hell for 1v1 fighting gameplay.
2nd place would be Katamari Damacy for its beautiful simplicity - just the 2 analog sticks are used.
Everything about that UI was great because it was in universe. The breadcrumb trail being a laser you pointed at the ground, your inventory being a hologram projected from the suit, your health being a literal bar of health on the back of the suit, all of it worked so well.
Cod BO3 zombies mode is so simplistic and non intrusive. Not to mention all the important specialists are all combined on the bottom right side for you to see clearly. Aesthetics also deserve credits as well.
You could go with the clean minimalist look or you could go for the complete opposite.
For one that's unironiclly good I adore highfleets top down view
