I came here to say this! These games are highly underrated. Amazing story and world building, actually having to be sneaky even with low level enemies, amazing music, these were always my top faves.
I must admit I've never seen or played these. They might be a bit too new for me. I listened to an interview with the game designer on the retro hour a while back. It sounded intriguing.
Would you care to give an elevator pitch on why these are must-play?
God I remember having to actually disable enemy AI to get through The Cradle as a kid.
Thief 1 and 2 have incredible community made mods that completely overhaul the graphics and make it quite a beautiful game. Said community is still alive and well over on the TTLG forums, making fan missions for the game to this day (including the highly regarded Black Parade, which is basically an entire game made in the dark engine).
The only stealth games I've played that come anywhere close are Dishonored 1 and 2 (which, unsurprisingly, had a lot of Looking Glass veterans working on them).