This is a hard question to answer, because the really unfun ones either get dropped so fast I forget I ever played them unless someone jogs my memory by naming them directly, or I'm willing to just shrug and say "this is probably great to some people, but it's not a genre I like." I guess for this category, I would point to The Witness. I heard so many recommendations for it, but aside from the occasional "oh, neat" when I saw how a puzzle was placed in the world instead of on a board, I couldn't tolerate it for nearly as long as it wanted me to keep doing the thing.
The game I memorably should have enjoyed - that I had the highest hopes for (and the biggest subsequent disappointment for) was Hellblade: Senua's Sacrifice.
At first, I loved the deeply disturbed main character and grim Norse fantasy world being crafted around me, but the combat felt so disjointed from the story (on purpose) that it felt like there was one guy on the dev team who liked combat who everyone was afraid to piss off, so they had to make concessions and put one token immersion-wrecking battle in every so often. And it's mad that Senua has two entire character traits - "psychotic" and "warrior" - and one of them managed to feel immersion breaking.
Then the ending destroyed the bits of the game I DID like and made me feel like a tool for ever having bought into the grim fantasy world to begin with. That shit is everyone's most hated ending trope, and I walked away from the game feeling like I'd wasted my time.