Thief 1 and 2. The controls & mechanics feel clunky to the uninitiated, but after learning them they're still ahead of everything that's come since; Especially

Thief 1 and 2. The controls & mechanics feel clunky to the uninitiated, but after learning them they're still ahead of everything that's come since; Especially in the sound design department. If you can get past the graphics they're truly a peak in single-player game design. I recommend starting with Thief 2 though, it's a bit more beginner-friendly. For best results, play from the start on Expert and just save scum while you experiment with how it all works. Expert mostly increases difficulty not by making enemies hit harder, but by giving you more stuff do do/incentive to explore.