The dark, disturbing hell-based theme, coupled with distinctly memorable soundI was a huge fan of the original Doom back in the day, and for me it is one of the greatest games of all time. I mostly played either the shareware version, or the final version of the game, The Ultimate Doom, which was a '95 re-release. It added in a 4th Episode to the game that was fought in a city on earth which led up to Doom II, and also added the Doom 95 launcher which allowed you to run the game in 640x480 (as well as any other Doom games or .wads) with Windows 95 or better.
effects from doorways opening, to hissing, howling and gnashing creatures, put
atmosphere in the first-person shooter genre. Doom was packed with dozens of
levels, awesome guns (the shotgun, plasma rifle, and BFG, for example) and
adrenaline-pumping action. You couldn't look up, but it didn't matter. The game
challenged your skills, saturated you with then-awesome graphics and sound, and
genuinely burned into your subconscious.
The Ultimate Doom (and Doom II) came with the Collector's Edition of Doom 3 for the Xbox, and I've replayed through it once and have already started a second time. I've lost count of the number of times I must have played through The Ultimate Doom, and even today, it remains as fun, intense, and addictive as it did a decade ago.