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?
Bastion was huge when it came out. It definitely got forgotten after a couple years though.
I still have it on several devices, like the old iPhone, an iPad and a PS Vita, I haven't got to play it yet :(