This is not gonna be an ordinary answer to this thread, but...
Arise 4.
The fourth and final (and worst) game of the (already awful) Arise series of flash games on Newgrounds, Arise 4 took everything wrong with the first three games and made them even worse. And I happened to discover them while in a hotel room in Great Britain. The worst mechanic was the combat sections; randomly, floating heads will appear and float slowly towards you, you need to shoot all of them with the worst gun ever added to a video game. The gun had incredibly slow input delay, a crosshair that was only correct if you aren't moving, and no mouse boundaries, meaning you could easily click out of the playable space and then you couldn't fight back. If you miss a single floating head, you die and have to reload the entire game.
The catch? While playing, the internet suddenly died at my hotel. I called the receptionist (while still shooting these neverending heads with my other hand) and she confirmed it wouldn't be fixed till morning. So if I died in-game, that's the end of it.
I played for hours; the playable space is a hedge maze, impossible to tell sections apart from each other, the puzzles were nonsensical "just use things randomly until something works," and there were tons of items hidden behind invisible pixel-hunts. And those goddamn one-hit-kill faces kept appearing throughout the whole game. Eventually I booted up my Amazon Kindle (generation 1, which came with free internet anywhere on the planet, even if it was almost impossible to read webpages on its tiny screen) and suffered through following a text walkthrough, which was just barely easier than continuing to brute-force my way through.
And then the final boss was a giant floating head you had to kill
forty-eight times, which should have been hard except I had a PhD in that game's terrible combat system by that point. Never gonna have another gaming experience like finally beating that game and closing the computer down for the night.
