Usually, when a game disappoints me, I tend to get disappointed during the latter half of the game. However, there have been a few exceptions where I had instant buyer's remorse.
The Legend of Zelda: Breath of the Wild. It looked amazing in the commercials, but as soon as I started playing, I realized that I would never be able to get rid of the weapon degradation, and that the cooking/crafting system was basically mandatory. Add to that the braindead dungeon design and the copy-paste shrines, and I was sick of the game long before I finished it. I beat it and will never play it again.
Dark Souls 2. I still don't know how the creators of Demon's Souls, Dark Souls, Dark Souls 3, Bloodborne, and Elden Ring managed to make a game this poorly designed. I slogged through this game for 120+ hours and beat it just to spite the game. I will never play it again.
And just recently, South Park: Snow Day. Unlike the previous two South Park games, this one is a 2000s-style low effort cash grab licensed game. All of the budget seems to have gone into the visuals, since those are the only part of the game that's any good. The game consists of only 5 missions/chapters, during which you do nothing but mow down waves of identical enemies Dynasty Warriors-style. There's no longer any exploration of any kind, and all of the missions have the same basic structure except for the third. Combat is extremely barebones, as there are no longer classes and only 3 melee weapons and 3 ranged weapons. And the game is freaking hard. I would have beaten it in less than 8 hours if it wasn't so damn difficult. I gave up playing on normal mode after Chapter 3, and this is coming from someone who beat Dark Souls 2 and has reached the final boss in RE3 Remake Nightmare Mode. What really makes it a pain in the butt is that if you die, you have to restart that entire mission from the beginning. I just beat it, and now it will sit on my shelf until I can give it to a co-worker who wanted to play it, as I have no intention of ever playing it again.