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?
Nightdive Studios (they, among other titles, remastered System Shock, which has received pretty good reviews) wanted to remaster Eternal Darkness, but Nintendo - who owns Eternal Darkness - doesn't want that to happen.
Also, the original developers of Eternal Darkness want to create a spiritual sequel, but that seems to be… an eternal project. Check out Shadow of the Eternals, if you want to follow that project. There's a gameplay video from like 2013 or 2014.
Haven't they tried to get the spiritual successor off the ground on a bunch of different occasions? Are they still trying?
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.