Generally:
Parchment put in all places where it was originally in WH1 and WH2.
Turned of that obtrusive flame/smoke effects for many common components (the ones used by WH1 and WH2 races).
Top right dropdown buttons are round again.
Provinces dropdown list is the same width as the other dropdowns again. There may be some overlap in provinces with allied outpost now but nothing too extreme.
Changed the orange font color used for many titles and subtitles (introduced in WH2) to brown as in WH1 which fits better the overall UI in my opinion

Main Menu:
- main menu slightly reshuffled, added parchment and frames around some buttons and individual components.
- the lord selection movie is now inside a frame with locked aspect ratio, making it smaller but at least it's not getting stretched and deformed now
- I focused mainly on campaign selection screen. The other screens would probably appreciate a bit of sprucing up but I lack the motivation to do so at the moment
- improved resolution of WH1 still backgrounds
- added the overlaying smoke shader over the background image/video that used to be present in WH1 that used to make even the still images look like they're slightly animated. At the moment, the shader is active for all backgrounds. At first, I thought it's going to be too obtrusive but I actually really like how it looks even on top of non-WH1 backgrounds. I'll try and find a solution to have it active for WH1 backgrounds only if enough people complain but until then, I'm leaving it as is

Recruitment panel:
- pretty much as original

Unit information panel/tooltip:
- pretty much as original
- removed the expand/collapse buttons as I fail to see a use for them
- removed the option to see abilities listed below each other. It was a huge headache to make it working with current UI and ultimately wasn't worth it

Character details panel:
- managed to bring back the animated subtitles in the left panel containing character details/effects. However, instead of three short windows with sliders it's only one now.
- behind the character 3D view is now a race specific, faction colored background to make the window look less empty/dull and slightly more personalized
- I had to improvise with the right screen equipment part so hopefully you like it
- skills tab is pretty much as original
- quest tab - each quest has it's own original parchment
- removed the expand/collapse buttons as I fail to see a use for them
- removed the option to see abilities listed below each other. It was a huge headache to make it working with current UI and ultimately wasn't worth it

Technology panel:
- pretty much as original
- tree dimensions slightly changed by CA and is a complete nightmare to work with, unfortunately so editing that is an asspain. This is the best I could come up with

Objectives panel:
- victory conditions pretty much as original
- quest tab is new so now it's parchment everywhere

Prebattle/Postbattle screen:
- pretty much as original

Battle:
- pretty much as original
- speed buttons are round again
- managed to restore original winds of magic container. Now it's easy to read at glance again!
Maximum value is now 100 instead of 30 like in WH1 and WH2.

Diplomacy panel:
- pretty much as original

War coordination panel:
- complete freestyle. Now there's a lot of parchment

Faction panel:
- pretty much as original
- in place of that stupid 3D view, there's a movie now like it used to be in previous games. LLs that got released first with WH1 now have their original movie back (faction panel only, lord selection is the new movie)

Rites panel:
- pretty much as original

ESC menu:
- mixed a bit of original with the new. Gone are the large buttons for settings now. Now every buttons is the same

Province panel:
- pretty much as original

Building Browser:
- pretty much as original but something doesn't feel right. Can't put my finger on it. Let me know if you have any suggestions

Lord/Hero recruitment panel:
- pretty much as original

Factions specific panels:
- panels such as beastmen panel, Shadowy Dealings, Alith Anar, Grom's cooking etc. have been changed/remade to look like their originals. Beastmen panel was especially pain in the ass.
- Shadowy Dealings, Ikit Workshop, Grom's Cauldron, Taurox panel etc. had WH3 buttons instead of their respective unique DLC ones.
- Grom's Cauldron on the top bar wasn't working at all as a button, as it used to WH2, even without an active dish. Now it's fixed
- Beastmen Panel had completely different buttons (like Chaos Dwarfs) and animations, which work as a feedback after button click, were not functioning at all. All that has been fixed.
- Alith Anar was missing its animated background. Now it's back.
- Forge of Daith was missing it's original nebula-like background.
- and some other changes I don't remember

Some components that used the have alliance coloring now don't have it and stay green at all times (e.g. comparison labels in unit information tooltip, balance of power meter). I'd ideally turn it off for health bars as well but that one is somehow hardcoded, sadly.

Nuance to WH3 factions - Kislev, Cathay, and Chaos Dwarfs have recolored version of WH1 leather textures (can be seen in recruitment and character details panels) while the others (chaos and ogres) have recolored version of WH2 leather textures.

Managed to fix a few bugs left by CA such as unit information tooltip not changing the unit category icon to their respective categories (such as renown, state troop etc.) or beastmen panel not playing animations at all.