Age of Wonders 3 is really good (and not made by Paradox, so there's only one DLC)
Crusader Kings 2, Age of Wonders 3, and Europa Universalis 4 headline the Humble Paradox Bundle
Paradox Interactive is the power behind the throne that is the latest Humble Bundle, which kicks off with Age of Wonders 2: The Wizard's Throne, Darkest Hour: A Hearts of Iron Game, Magicka 2, and Crusader Kings 2 for $1. Crusader Kings 2 is the big one in that package: It normally goes for $40 (although it's currently on sale for $10), it has a "very positive" user rating on Steam, and people have literally played it for thousands of hours. Steam user Dylan, with 1046.5 hours on record, called it the "best way to waste yer life while sitting on a crappy chair eating ramen pride noodles," and you're not going to do better than that for a dollar.
If you have more than a dollar, however, you will. Beat the average of about $6.50 and you'll also get Age of Wonders 3, the Crusader Kings 2 expansion The Old Gods, and Europa Universalis 4, another massive, dense strategy game with the potential to become the last game you ever buy: Comrade Dongo, with 3867.9 hours played, called it a "10/10 experience," although his reasoning is a little unclear.
At the top of the heap, for $12, you'll add Steel Division: Normandy 44, the Age of Wonders 3 Deluxe Edition DLC, the Magicka 2 Deluxe Edition DLC, and the Europa Universalis 4 expansion El Dorado. Normandy 44 isn't quite the timesink of some of the other games but Steam user Zagskrag has sunk 864 hours into it and has "definitely had a lot of fun."
Paradox games aren't necessarily the most mainstream, but they tend to be outstanding strategy experiences for those with the patience to get into them—check out our reviews for Europa Universalis 4, Crusaders Kings 2, and Hearts of Iron 4 for more on that—and if you're curious, $12 (or less, if you're not hung up on the deluxe DLCs) is a good way to get started. The Humble Paradox Interactive 2019 Bundle will be available until February 19.