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DOOM (1993)

Truely remarkable and timeless game, Knee Deep in the Dead is flawless. Would be a 10/10 if the game didn't have invisible pinkies, Lost Souls had less health, and if the Spider Mastermind was a more compelling final fight (though understandable, since the alternative would have been the fucking Icon of Sin. Fuck that shit. Ruined DOOM II for me even more than the nosedive in level design).

Playing old community levels and the TNT expansions also opened my eyes to just how much shitty level design can ruin the fun. There's no worse feeling than pressing a button and not knowing what it does.
DOOM mapping should be the Turing Test for game design imo. If the best level you can make is Barrels O' Fun, go be a plumber.