Stalker: Call of Pripyat is worth a try. It is a shooter but it is free roaming with missions so a bit more open plan than a corridor shooter. I don't play many games like that anymore though, I got burned out during the Wolfenstein 3d era. For me that was the pinnacle of single player shooters. I try occasional ones though.
Call of Juarez I really enjoyed, but I tried the sequels and hated them. They tried to become Call of Duty and I preferred their original idea.
If you don't mind playing older stuff, System Shock 1 and 2 are some of my favorite games of all time. They are as much RPG as they are shooters though and quite old now. Vampire Bloodlines is similar.
The only shooter I play nowadays is Arma3, but I play it mostly for one specific mode (CTI) because you start of shooting, then progress to driving tanks and vehicles and ordering squads around, and eventually you fly gunships and jets. That's the game for me now because it is just so huge. It can be played single player too, it has a good campaign and lots of single player missions and you can download more user made missions or make your own.