Amazing stealth game and very deserving of its reputation as a classic. The stealth mechanics are great for their time and still just as good now. The sound and darkness detection systems are incredibly well done, and the tools you're given are a ton of fun to use. I really love the mission variety as well. The game has a pretty even mix of both horror-themed monster ruins and typical thief missions, and they're both thrills that reward thorough, patient exploration. The writing is also very charming throughout the whole game, both the cutscenes with their unique visual style and the conversations and idle dialogue you can eavesdrop on during missions. Truly fantastic game all around and one of the greatest games ever made. Very cheap on sale too. Just remember to install Tfix to fix some issues with running the game on modern hardware as well as a stereo sound fix.

As good as it might have been for the year it came out, it might not be so worth playing now.
Where the game shines the most is with it's stealth mechanics which I liked, giving the player the necessary tools, encouraging being aware of your surroundings and avoiding combat whenever possible. It's easy to see how this set the bases for what many stealth games later would follow.
What holds it back is a fairly outdated level design. A lot of areas are bigger than they should, having a certain amount of empty space and making it easier for the player to get lost. It doesn't help that you are given little to no direction on where to go and a map that only makes it more confusing. This just made the game frustrating and no fun.

⠀