Alan Emrich, then Computer Gaming World’s Online Editor, gave Master of Orion an XXXX rating when previewing it in 1993 as a cheeky way of describing the essential elements of the strategic conquest game: eXplore, eXpand, eXploit and eXterminate.
(The term was changed to “4X games” to accord it some decorum, which is a good thing because the phrase “XXXX strategy games” brings to mind “Sid Meier’s True Anal Stories” and nobody needs the associated mental imagery.)
But four Xes might also describe the experience of playing any given 4X game. The player must explore the complex ruleset, experiment to realise their strategies then extend those strategies to cope with playing the game at higher difficulty levels.
The fourth and final X of the player experience is exhaustion, which inevitably sets in after sinking dozens if not hundreds of hours into campaign after campaign. No matter how deep and expansive the 4X game, there eventually comes a moment when the one-more-turn compulsion is replaced by ennui.
Even the Civilization series, the standard bearer for 4X gaming, is not immune to this. Anyone who has been with the series since the first game is entitled to feel a little jaded two decades later. The rules may be tweaked, new mechanics may be added, the presentation may be improved but the Civilization experience is fundamentally the same and at some point the thought of having to rediscover Pottery for the umpteenth time simply crushes the spirit.
Fortunately, Firaxis anticipated this so the fourth game in the Civilization series was deliberately designed to be highly moddable and this led to some outstanding fan-created variations on the basic Civilization formula.

(Image source.)
Fall from Heaven 2, developed by a team of 15 led by Derek “Kael” Paxton, is arguably the best of the lot. It’s the perfect mod for those who appreciated everything Civilization IV brought to the table in 2005 but couldn’t get much into it because they’ve just played too much Civilization. The mod’s greatest achievement, and it is a considerable one, is returning the joy of exploration and experimentation to the jaded Civilization player.

