If you haven't played the various Bethesda games (Oblivion, Skyrim, Fallout), now is a great time. There is a modding tool called Wabbajack that auto-installs curated lists of hundreds of mods, all patched to work together, and you can get an incredible setup with very little work.
It depends on the wabbajack list you use. Many bring the UI more or less in line with modern standards. Most of them include major graphical improvements. Then they bring new content on top of that - items, spells (if applicable), creatures, NPCs, etc. rarely, they also expand the game maps with new areas.
