Caves of Qud is one of the best exploration games I've ever played. It's a traditional roguelike where the overworld map is the same each time but the world history, factions, and most individual zones are procedurally generated each time you start over.
You play as either a mutated human with strange bonuses like extra arms, the ability to mind control, wings, etc. or a Truekin that starts with higher base stats and the ability to use implant tech to do things like replace your legs with tank treads or your eyes with night-vision goggles.
It's a deep simulation; all of the NPCs in the game are as fully modeled as the player character, the NPCs you meet are a result of the generated history, and the best choice is often to run away.
It's turn-based with multiple difficulty levels. I recommend playing on classic, but the other ways are just as valid.