Well if you're into grand strategy then anything by Paradox; personally my favourite is Crusader Kings 2 and I've been playing a lot lately, but there's a lot of love for Hearts of Iron III and Europa Universalis IV from their fanbase. If you want something a little less taxing then Civ V if you don't already have it is great for taking up any free time you have, and then the free time you don't have too. I wouldn't bother with Beyond Earth, though. It's good, just not worth the price tag. In the same vein as these games, the Total War series is always good for time sinking, although Rome II is still probably best to avoid. Medieval II and Empire are my favourites, closely followed by Shogun 2.
I've also been playing a lot of Red Orchestra 2 (WWII Soviets vs. Germans shooter) multiplayer, which I always go back to. Personally I think it's the best WWII shooter out there. If you want something more tactical, then ArmA 3 is pretty damn good. If you want some with a little less realism, then Insurgency is a great multiplayer (think Counterstrike mixed with a bit of Battlefield). Sniper Elite V2 and Sniper Elite 3 are damn good fun if you're into WWII sneaky sneaky times. If you want frustrating sneaky sneaky times then an oldish but good game is Death To Spies. Some people hit and miss with it though, I personally really enjoy it, but I understand why others take issue.
If you haven't picked up Middle Earth: Shadow of Mordor then do asap. In my view it's the best Middle-Earth based game by far. Satisfying combat, and it looks great too. If you want something more chilled, though, you can always flood a city or two by building dams in the wrong places in Cities: Skylines. It's seriously so much fun, I've been playing a shit ton recently. It's currently my go to game for when I just want something casual.
This is becoming an essay now so I'll stop there. Hope you don't (or maybe I hope you do) have those suggestions already!
