I'm in the middle of a pretty deep UX and UI grind, it's nothing interesting for the devlog which is a shame, but as a web-developer I know that it is indeed super-important - I'll happily spend a good few hours experimenting with menu layouts etc.
For the www one of the easiest measures is the "number of clicks" it takes to do what you want, each can take a lot of programming and add a feature most would argue is superflous, ie:
- Automatically Focus the Login Form
- Take the user to the most accessed page when first entering the site
- Extend the login sessions to last 120 days instead of 8 hours
- Default settings should suit common requirements
etc. etc.
With games I'm coming across the same ilk of tasks that (as you have hinted at) aren't part of the glamour of gamedev:
- My progress syncs across devices / platforms
- I can find my friends on the game
I remember Liero having a very stable multiplayer server / client system at a time when most games got it wrong, it would be difficult to enjoy that game without that foundation of greatness.