I loved Blacklight Retribution. It's been so long delisted that my most unique achievements from it disappeared from my profile. One was 0.01% of all players.

It's surprising that it doesn't seem like the X-ray mechanic (which is the main thing I remember from that game) was really picked up by any other game. There were way fewer cheating accusations than in other games, because what would normally be a "cheat" was a core game mechanic, and IMO that made it really enjoyable. It's a shame that game died.