Now, I am not going to count games that I knew were bad beforehand but still deliberately played to see how bad they were, I am going to assume the spirit of the question implies starting a game and the realization of how bad it is slowly kicking in.

One game that came to my mind was "Conspiracy: Weapons of Mass Destruction" on the OG Xbox, but there's probably worse games I played but have forgotten about.

Disregarding the absolutely unplayable and broken, I think it's a toss up between the 2008 Alone in the Dark or Final Fantasy 15. I'm more inclined towards the latter because I haven't played the former since release. It's just a godawful RPG, if you can even call it that, the game basically plays itself, has no depth whatsoever, the open-world is meaningless and empty of anything interesting. Not to mention the story is both dogshit and a confusing mess nonsensically split between different DLCs, movies and god knows what else. Definitely the worst big budget RPG (again, if you can even call it that) I've played so far, it's borderline insulting. The worst of it all? It was my first Final Fantasy and it was so bad it killed any interest I had in the series.

Recently... Deadlock

Aw yeah bring on the downvotes

The Lion King.

Wrestslemania x8 on the gamecube. Didn't even have a frigging campaign mode...

Cauldron 2 for C64 you start playing and find out you have no clue how to progress the game.

Bubsy 3D. The controls were awkward, the platforming was horrendous, and the levels were nonsensical.

"Worst" by technicality - I actually had a lot of fun with it for several minutes:

This famous piece of internet lore.

At the time I tried it, it worked "perfectly" in Wine (as well as on Windows that is)

Quest 64. It wasn't even funny bad, it was just boring.

There are a couple console games and one in my steam library that absolutely come to mind. As for which I think is worse is definitely up for debate because I think I dislike these 3 equally, even if I can only remember why I dislike two of them.

Don't remember the exact entry, but I borrowed a Dynasty Warrior game from my brother (who didn't like it as far as I'm aware) for xbox360 and something about it I just didn't like at all. Then there's Worms Blast. For a spin-off of worms, that from what I remember just feels like a worse bubble bobble style game, I was absolutely disappointed.

The Steam game is Macbat 64. By no means is it unplayable, add riddled, or full of annoyances preventing me from playing, but I beat it in less than 50 minutes. It's a 3D platformer whose relatively small levels pay homage to other games, but it just wasn't fun for me due to lack of content I was interested in (longer levels with more going on) when it comes to 3D platformers.

Flatout 3. I just checked on steam, and it's tagged as "psychological horror". Being a fan of the first one, and still having spent lots of hours playing the second one, I was totally not prepared for the utter monstrosity of the third one

Myst.

I came for the graphics and because I liked adventuers. Was disappointed by the static graphics and I didn't understand what to do at all.

C&C4, hands down. Single handedly murdered the whole franchise.

Edit: to be specific, I took this to mean “worst game by a major publisher”

I must've played a ton of trash games that I purged from my memory, but one notable one that comes to mind is Command & Conquer: Tiberian Sun. The game was super highly anticipated and hyped and I was a massive C&C fan before, only to be completely disappointed by this massive turd that they shat on this genre defining franchise. The revolutionary "physics" did nothing to the game play, the main story was maybe a total of 4 hours and it was just buggy as fuck with the AI pathfinding being incredibly bad and somehow worse than the predecessors or the main other RTSs of the time.

probably that Tom Sawyer game on the NES. like, wtf even was that?

The 4th game i made public

Its a mobile game where you have to find 4 "hidden" painted eggs. It was supposed to respawn the eggs in different spots, but i dont think i ever tested the game so i didnt know it didnt work.

There is also a score that doesnt work and a high score that cant go past 40

This is the game i spent the least time or effort making, copying everything from the last game i made, but changing the textures and modifying the part of the spawner of the collectables where they spawn randomly on the screen to appear at one out of a set of positions

My first thought is The Fortress of Doctor Radiaki for DOS.

A game I never played but is still memorable is early 2000s there was a game in Babbages in my local mall called "Prison Tycoon" that had a cop beating a black man on the box.

RUSH’N ATTACK for NES. I remember buying it as a child and being devastated that it sucked so bad.

Evergrace. Half-baked and outdated in every way. Life is too short to play bad games just because they're cheap.

Shadow Madness on PS1. Unlikable characters, incoherent story, bad graphics, and boring gameplay. It was like someone drew a better JRPG from memory.

Sea of Thieves.

That game is too buggy over the years it exists to be as popular as it is, and not in a "haha smol glitch" buggy, but "lets disconnect at the WORSE possible moments" (like you having a ton of loot).

Not worth it. A waste of 30 bucks.

Gotta be Seven Samurai 20xx

https://youtu.be/MKA5Xvrm9WQ?si=krSoMAv58hSycsur

Mega Traveller 2. Buggy janky story. Bad combat. Character creation that includes all the skills from the pen and paper game but only about 10% of them actually do anything in game.

https://en.m.wikipedia.org/wiki/MegaTraveller_2:_Quest_for_the_Ancients