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 have tried twice. And yes, they still want to make it happen. But last time I heard the team made a game they need to support for few years (some kind of online game), so it's going to take some time before they can try again.