I know this will sound insane but I liked the metro tunnels of Fallout 3. It was fun (in a weird way) to get lost in them after taking a wrong turn, and discover an outpost of zombies or raiders or ...

Got Tale of Two Wastelands up and running - took a couple hours, but the setup walkthrough is quite detailed. So far the only extra mod I've added so far is a quickstart, because fuck sitting through ...