I'll go with
Privateer 2. Buggier than the Colorado River at the height of mosquito season, but one I have a soft spot for all the same. It suffered from a rash of arbitrary and hair-pulling crashes, often mid-flight (or worse, when landing) which erased all in-mission progress. No in-flight save feature, you see. Sometimes even saved games would mysteriously become irrevocably corrupted when you loaded them-- the game would
always crash during the next mission (regardless of what mission you'd accept, even if you tried detours, switching destinations, and such to "trick" the game), and thus rendered them utterly useless. And unlike other notoriously buggy games released in the late 90s--early 00s period of gaming, there was no comprehensive fan-patch ever assembled to save its fans from its myriad of bugs. Probably because there was no real Privateer 2 fanbase, and most of the bugs were probably un-fixable.
Still, I loved it (much more than Privateer 1, which most Origin fans prefer by a landslide), mostly on account of the vivid, edgy cyberpunk world which came alive in elaborate costumed and be-propped Mise en scènes boasting very solid thespians, including many "name" actors like Christopher Walken, Brian Blessed, John Hurt, Jürgen Prochnow, and of course, Clive Owen, in colorful dives, apartments, night-clubs and posh offices all across planets in its particular game-world. Quite a bit of detail and background went into all the people, places, and clans of the "Tri-Star" system you could read about in the database; I'd argue at least as much as any Wing Commander game. I think all the FMV production values and writing were really stellar, and deserved a far better game than the broken and mediocre space-sim engine we were given. I wish the game world, characters, plot, and cyberpunk flavor of Privateer 2 could be transplanted into, say, Freelancer's engine.
But mostly I just wish GOG would release it here, warts and all.