There were silly ones like the one making your characters head larger for each kill, and those which made it just different like low gravity, and so on.
It was also relatively easy to make your own, thanks to UnrealScript.
Really wish more multiplayer games embraced this concept, it really increased replayability by changing things up.
Separately it's a shame most modern games have removed LAN gaming.
I just wish these groups making fan-made builds would share at least patches, so they don't become gatekeepers and others could build on their work.
Sign me the f up!
I've been missing a lot the frenetic gameplay of those, used to play a lot of UT at a decent level but nowadays I only see tactical FPSs or the likes of Counter-Strike/Battlefield with a high player count.
This one is the last one I heard of but I also haven't followed the scene much lately: https://store.steampowered.com/app/324810/TOXIKK/
I think the closest I got was The Finals but still class-based, so reminds me more of Team Fortress.
I loved playing 1v1 on Quake 2/3 and UT, also team deathmatch, from the list you commented it feels like each game got one of those aspects but none that makes the genre of UT what it is: knowing where weapons/ammo/armor spawn, map knowledge to navigate around, emergent movement mechanics (rocket jumps, strafe-jumping, etc.).
Interesting to see this genre mostly died out, and remnants of it have been scattered across other genres.