Those who like Crusader Kings II like it a lot, but it's far from the most accessible game ever. It's a generations-spanning grand strategy game that sees you establishing and expanding a kingdom, but the attention to historical detail is frankly, quite intimidating.
The game is distinctive in its simulation of dynasties, which lets you control your lineage across generations from 1066 AD to 1453. Additional DLC allow for earlier start dates, but the strategy remains the same: the use of war, marriages and assassinations, etc. is necessary to achieve success for your dynasty, whether you're playing as one of over a dozen different historical figures or one created from the "Ruler Designer" DLC
Like Sid Meier's Civilization, success in Crusader Kings II is mostly player-defined, though prestige and piety measures how well you surpass various historically relevant dynasties. The game ends when the player's current character dies without an heir or when all landed titles of the count rank or above are stripped from all members of the player's dynasty or when the game's epoch ends in 1453.
The game can be a bit obtuse about its own mechanics and the numerous tutorials and tool tips can still overwhelm you with a tidal wave of concepts and information. But for the next 48 hours it's free to install and play on Steam, and if you do that the game becomes yours to keep forever.
Crusader Kings IIcurrently stands at 82/100 over on Metacritic and has staying power among its buyers with thousands of concurrent players at any given moment. That's remarkable for a game that's nearly six years old. Also, it's the game with the best forum threads: