Well. What can I say? Revisited this with some trepidation, fearing it's brilliance back in the day would not translate to today's standards. By heck, I was wrong to worry. The majority of modern FPS developers would do well to learn from this all-time classic; atmosphere, challenge, frame rate, musical score and intrigue just keep me coming back 25 years later and the additional expansion packs make it a no-brainer. All hail ID software!