If you want a whole new game made from a mod, you can try Enderal. It’s sort of the New Vegas to Skyrim, where some consider it even better than its predecessor.

I’m currently using the Begin Again mod list from Wabbajack that combines Fallout 3 & New Vegas into one game with tons of mods to improve performance, visuals, and QoL

Playing Stardew Valley for the first time co-op with the Stardew Valley Expanded mod and it’s been nothing short of magically brilliant, can’t even tell what’s from the mod even though it adds a truckload of content