The first mature first person experience in that it offers gameplay that doesnt resort to killing everything (though you CAN do that, just expect to die alot!). First title to make use of 3d sound (and still one of the best) and be very important. "Sneaking" gameplay add to the spooky atmosphere (abandoned churches, dark wizard towers, zealot religious cults) in this game. Also lots to download for free for the game with a very devoted fanbase (new missions, mods). Also, it's not easy (compared to the average shooter), even on normal mode (the easiest mode) the game offers a challenge even to die hard shooter fans.