X4 - Foundations. I've played over a thousand hours of this game, and cursed it's name through much of that gameplay. On the surface it's a passable first-person space-flight simulator (in the loosest sense of the term) with combat, trading, and various missions. It also supports higher tier empire building and strategy, which I've found the most compelling, but that aspect is often at odds with it's first-person nature. I grit my teeth every time I've had to interrupt the act of building out a new station or coordinate an assault on an enemy system in order to personally save a single transport ship from a pirate/Xenon/Kha'ak attack because no matter how good or how many NPC escorts I hire they are never adequate. And if you lose a ship, good luck figuring how which station or trade routes it was servicing. The one saving grace was the ability to pause the game in order to do things like designing a station or directing ships without the concern of being interrupted. Naturally, this drags out the game significantly.
Other major detractors are the clunky, thoroughly inadequate UI (yes, there are mods that help, but they never go far enough) and the laughably bad missions. However, I must stop myself here or I will end up writing a lengthy thesis on this game.
Suffice it to say, it's a flawed, but oddly addictive game.
Every time I fire up X4, I play for an hour or two, get frustrated with it and go back to X3 instead. I don't think I've ever even left the first area of the map because the first couple of missions require obtaining things that are only sold by pirates and also it's RNG whether a place has it or not.
I don't think it's that bad compared to X3, in fact I would say X3 is a better candidate than X4 for a "love/hate" award due to the almost constant jank and the... harsher consequences of unplanned rapid deceleration.