Simply one of the greatest games of all time, first game since Half Life 2 that's changed my expectations of what a game can be. It has some of the finest level design I've ever seen. The combat is slow, methodical, and intense. It's challenging but fair, you realize your mistakes as soon as you die and have to learn from them. All the different classes and builds give it
near infinite replay value (along with NG+). It's spawned an entire genre for a reason and is more than worth your time and money.