Even though I usually watch reviews to avoid playing bad games, I have played some stinkers over the years:
Dark Souls II:
Dark Souls I and III are hard because they're designed to be challenging. Dark Souls II is hard because it's poorly designed. The game was handed to a new team who didn't understand what made the first game so great, and the result is like playing those 'extreme' fanmade Mario Maker levels. An overpowered early-game boss who stalks you throughout the game Nemesis-style and respawns if you do manage to kill him, bosses with 12 hard-to-kill enemies standing between your last save point and the boss door, a swamp with so many powerful long-range magic enemies in it that you can only cross it by running from cover to cover like it's Vietnam, and that's not even half of the BS. I may be a fan of soulsborne games, but I hate this one with a passion. I regard my clear data as a trophy, because I will never play it again.
Tomb Raider III:
Same story as Dark Souls II. New team, didn't understand the first 2 games, made an overly aggressive F-You of a sequel that salivates at the thought of screwing you over. And they didn't even have the decency to polish what they made. There are genuinely game-breaking bugs in certain levels.
Resident Evil 6:
I think Capcom was taking too many cues from the mediocre live-action films when they made this. It plays like a bad hollywood action movie. There's never any sense of horror in this game, only action setpiece after action setpiece. There may be a lot of different campaigns, but only Leon's is any good, and even that is mediocre at best. Some of the final bosses are horribly designed as well, especially the big mutant bug you fight as Leon. In its final phase, there are lightning rods on the floor, and you have to stab the bug with them under specific circumstances so lightning will strike it. Not only does the game not tell you this, it gives you zero indication of how or when to use the lightning rods and the boss just keeps regenerating if you don't.
Valhalla Knights:
Probably the most poorly designed RPG I've ever seen. The sound design is so bad that just listening to your character walk around grates on your nerves. Bought this for the Wii over a decade ago, played it once for an hour, then never played it again. Just bad, low-effort game design.