I've been recently been thinking about Arkane Studio's Prey which is a immersive sim, with a pretty good rogue like dlc, that probably has one of the strongest hooks of any game I've played. If you liked Halflife, System Shock, or Deus Ex it's definitely worth a play.
Are there any titles that might not have been commercially successful that you feel everyone should give a shot?
It still is a little lib-ish. The game goes to great lengths at showing Silverhand (and anyone blaming capitalism) as being a bit too harsh or off their rocker, with V explicitly mocking his leftist opinions in dialogue many times (replaying the game, once during an elevator ride, another after dealing with the chapel in pacifica). The game is very on the nose about blaming corporations but spares the rod when talking about the system.