One of the best strategy games that you can get your hands on is now free to play. Paradox has just made Crusader Kings 2 free forever on Steam, so there is no excuse for you not to try it out now. A word of warning though: some players are showing over 1,800 hours of gameplay, so be careful with its addictive and free-form nature.
Crusader Kings 2 isn't a game about graphics, and it never was; when it released in 2012, it wasn't anything to brag about visually, but the incredibly deep core gameplay. However, you should be ready for a steep learning curve as this is a game with so much to learn and explore.
Of course, Crusader Kings 2 has quite a few paid expansion packs waiting for you in case you like the base game. It should be a long time before you decide to get the expansions, though. There is even a Game of Thrones mod in case you want to live the gory adventures from George R.R. Martin's book and HBO series.
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