I'll go very offtopic, and just say that my first 3d First person shooter was DN3D, and only afterwards I got my hands on doom... which I liked more. But at the time, I was amazed by the whole first person shooter idea.
Also, this was my first ever PC game. I played it for years. I'm not kidding, YEARS. Still up there in my top games of all time along with ToCA 2 and others.