There was a game years ago called "Thief", which was novel, in that the opponent wasn't MOBs so much as light and noise, the environment you were in. I especially like sneaking in Lotro, but it's very crude obviously.

Fans of Thief apparently modified another 3D first person game to simulate the game-play, with more modern graphics, and just recently released a standalone version:

I've been trying it out (heck, it's completely free) and have been very impressed so far, there are oodles of fan created missions with various stories, detailed graphics, impactful sounds, stimulating strategies, some basic puzzles, etc. Note, although some missions enable you to go around like a hunter/sniper and you may have a sword, it's not designed to be a combat game, although some do play it that way, as you can parry attacks more specifically than in Lotro (auto-parry is on by default).

Anyway, it's been reminding me of sneaking around on my burg, but with more sophistication and object interaction, so thought I'd share. ;-)