Titanium: Well, by now it's about 50% truth and 50% a running gag anyway.
If anyone is wondering, the game is Mistmare. It was spectacularly broken at launch, got painstakingly patched to 1.7 for a fairly enjoyable experience, and then promptly devoured by the passage of time.
I played the $hit out of the Mistmare demo but when it came out I ended up not buying it due to how bad the full version reportedly was. I regret it to this day and have just arrived in this thread when I was checking if it is available on gog (I once tried downloading the abandonware version but couldn't get it to work). SO yeah, this is definitely on my list as well.
Also, everybody loved Unreal 1 but I personally liked U2 as well, so shoot me. I think the scavenger hunt theme sold it for me. Generally always like the whole franchise over the Quake counterparts.
Not sure if Metal Fatigue still counts since it got released on gog so some people must still love it just like me.
Rage of Mages 2: The Necromancer was one of the first computer RPGs that I've played and I loved it. I don't think I've met another person who even heard of it.
Fantasy General was my favorite of the SSI's General series. Though not sure if that one counts either since it even got a sequel recently, even if that sequel killed everything I liked about the game.
Diabolika - it's just a puzzle game but it's awesome, probably still available as abandonware.
Evolva was a very interesting and innovative game that did not get nearly enough recognition.
Fallout Tacticts, it got so much hate from fans of the first 2 games but I always loved it for the sheer fun of tactical gameplay and the fact that it was finally a Fallout game I was actually able to finish (many years later I was able to obtain the water chip and complete the first game but to this day I've never managed to find that goddamn GECK).
Not hated but definitely a niche game - Echelon, my favorite flight sim. In terms of difficulty it was the equivalent of Dark Souls but also required a joystick to be actually playable, hence the niche thing.
Gunmetal - a game that made you feel like a proper transformer, no idea why it got poor reception.
I kinda liked the Avatar game.
Finally from newer games - Mass Effect: Andromeda, yes it was of lower quality than previous entries in the series but to me it was still about as good as Witcher 3 (note, I played both after they have already been patched up but I don't hold W3 in as high regard as most, I liked W1&2 more).