Well then here's what I'll recommend:
The
STALKER games, mainly Shadow of Chernobyl and Call of Pripyat. Personally I prefer Pripyat myself but they're both amazing games the likes of which you wont find anywhere else. Atmospheric, intense, challenging, they're just an incredible experience to play. In both games cases I'd also recommend downloading the 'Complete' mod before playing as it essentially acts as a mega super patch improving the games visuals while also making them more smooth experiences. Later on if you find you like the series there are other, better mods out there for the STALKER games as well but for an introduction Complete works extremely well.
For another uniquely PC shooter experience
Red Orchestra 2 might be worth a try. If all you're used to are console fps then you'll have never played another game like it. RO2 is hardcore, one shot, one kill, war is hell brutality. It's also one of the most intense multiplayer games I've ever played, I can only actually play for an hour or two before I have to quit because it gets to me. The constant ringing from explosions... the screams of my comrades as they fall... the feeling of being trapped in a ditch knowing if I move even an inch I'll die...
It's as close to a PTSD simulator as you can get, Spec Ops notwithstanding.
And if you want something like Dishonored you could always play Arkane Studios previous game,
Dark Messiah of Might & Magic. Very fun game, I've always thought that much like their game before
that called Arx Fatalis, it deserved more attention than it ended up getting. Playing either Dark Messiah or Arx you'll see a lot of where Dishonored came from though and both are a lot of fun. I point out Dark Messiah in particular though since Arx is getting on in years and with a new PC, I imagine you'll want something that looks nice. And while it's not exactly a new game itself, I replayed Dark Messiah not long ago myself and it still looks surprisingly good.
For something more rts-y definitely check out Dawn of War 2 and Company of Heroes. Both games by Relic still look and play amazingly well, I can't recommend either enough, they're both fantastic.
And finally, truth be told, I wouldn't have really recommended Diablo 3. Both Torchlight 2 and Path of the Exile I consider better alternatives. Still if that's a type of game you enjoy look both those up, they're great fun.