The game itself isn't anything new, but the user experience is fantastic. Loved the idea of playing against a bot to determine skill before throwing the noobs to the wolves.
One of the best games ever created. Thousands of people still play it years after its release. It's become a national sport in Korea. And it's still damn fun to play. Amazing game.
The original Doom was one of my first forays into gaming, so I admittedly have a bit of id fanboy-ism in me. With that said, I can't bring myself to give Doom 3 above 2.5 stars. They just haven't improved Doom beyond a point and shoot game.