Do you know what sucks about video games today? Pretty much everything. But if you haven't played the original DooM late at night with the lights out and on Nightmare mode, you're a weenie.
What's great about this game? Everything. Set it on auto-run and you'll mow down demons from hell and anything else that gets in your way like a fuckin' freight train, man. Or you'll die and hell will rule Earth. Your choice.
Mindless entertainment, you say? Nonsense!
Get this: each room you enter requires a new strategy. Each combination of enemies you encounter requires lightening-fast thinking in addition to reflexes. You've got to learn how to prioritize, you gotta learn which weapons to use, when to retreat, how to retreat, when to utilize explosive barrels, how to use cover to protect yourself from one or more enemies while simultaneously flanking another... I could go on all night. Whenever I play a good old game of DooM, I feel the synapses in my brain popping like fireworks. If you don't, you're playing it wrong.
Never played DooM before? Forget playing it on DOS. Get Legacy here. Legacy is a program that updates the game, but in a good way, meaning it doesn't get all fancy. (Hint: you need certain files from DooM in order to run Legacy. You can get them for free. I don't remember how, but all it'll take is a bit of Googling.)
Check out this guy's video for more instructions: