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?
They were supposed to have a whole series IIRC, but the contract got cancelled because the initial offering didn't sell very well. It didn't help that the marketing didn't really know how they wanted to talk about the game.