Obscure, but Outcast (1999) was many, many, many years ahead of its time.
The graphics were absolutely INCREDIBLE for the time, even today in most games water does not look that impressive, adjusting reflectivity and transparency depending from the angle looked at, making realistic ripples based on the character’s motion… Bloom, lens flares, realistic terrain mapping, various rain/snow effects, depth of field, bump mapping, HDR effects, atmospheric lighting, anti-aliasing… This 13 year old game somehow had it all.
Also, the gameplay was really, really immersive and nothing short of amazing. I believe one of the first truly full 3d games with an open world gameplay – you could choose which missions you did and which order you would do them… Explore cities, mountains, forests, cruise around on dinosaurs (yep), have a chat with the NPC’s, even get drunk.
Also it was I believe the first game with an orchestral score. A really good one at that, performed by the Moscow Symphony Orchestra and choir (yeah, I had to look that up). The AI was considered revolutionary, maybe it still is. The story was emotional, leaving some players crying in the end.
Sadly it didn’t do very well commercially and remained in obscurity.