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?
No it wasn't… It was announced two years ago, they did announce the release date three days ago though.
Ah, details…What M137 said