I know that there were many more first person shooter games that came before, but this is the first one that truly captivated myself and many other people at the time. A PC from the early 90's wouldn't run anything that we all do today on our phones, but it ran DOOM, and myself, like many others were absolutely transfixed by this title.
Althought most people are probably familiar with the story already, you play an unnamed space marine that finds himself fighting the hordes of hell for some reason. There is a story in there, but mostly at that time we were just concerned with the action and horror. The tense situations including being able to hear but not see your enemies (at times) was truly terrifying at the time.
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look at those glorious pixels!
This game was so all-encompassing that it invaded my dreams and interfered with my studies. I would be in a boring lecture and then all of a sudden "snap back to reality" and realize i wasn't running down hallways that contain only 90 degree turns with a shotgun that I can reload alarmingly fast.
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learning how to enter "God Mode" kind of ruined the game
Obviously, in the 20+ years since its release, graphical capabilities have improved dramatically and the later Doom Games are even more creepy. However, the novel aspect of being one of the first games of its type made Doom an absolutely monumental game of all time. It is largely considered to be one of the best and most influential games ever made. I had played Wolfenstein prior to this, but Doom just seemed so much more polished.
FPS games are a dime-a-dozen these days. There are so many of them that I don't really even bother playing most of the ones that are released. However, when Doom was brought out in the 90's if you were into gaming at all, you played it and loved it, it was as simple as that. This is where it all began and if you look at really any list that can be taken seriously they will all state that this was one of the most important titles for video games.... ever!
I for one believe that is very true. I know that most of you were probably not alive or were very young when this came out, but it was really something to witness. We barely had internet back in those days and Youtube was just an idea in a person's mind at that time. When you played DOOM, you figured it out on your own. You tried over and over and over again to complete the game-which by the way does not have a happy ending even when you win.
It was an absolutely perfect game that solidified ID Software as pioneers in the industry and many believe that this title alone may have been responsible for the popularizing of PC gaming.