For me, the best game ever made.
Origionally played a pirate copy when it was first released back in 2000 just for something to do one night. I've then gone on to purchase the game maybe 3-4 times.
Completed the game so many times with every ending possible and I even have the soundtrack to the game on my phone. I can't remember the last game ive actually wanted to complete recently let alone several times.
The story line is absolutely fantastic, something games developers just dont seem to spend time on these days *cough* Destiny *cough* ...but also, the sheer volume in detail, there are so many hidden extras...like the Majestic 12 base hidden in the sewers in NYC. Modern games would have shipped that as DLC and it took me 3-4 play throughs to discover it.
One of the first games to offer a non linear play through, it gave you options on different ways to storm a building and even tested your morality by giving you the choice to kill or spare. I remember being amazed by being told off by your in game boss for going in the girls toilets for a quick sniff around, who would bother to code little things in like that these days?
Graphics are terrible now I admit, but pick yourself up a HD pack along with a copy of xpadder for joypad use and you'll quickly discover just how much you've been ripped off the last time you spunked 40-50 bucks on the latest console game.