The Division 2 - More of a "minor disappointment" I guess, as I still put tons of time into it. I just remember getting to the end-game that was supposed to be so expansive and amazing, but ultimately ended up being a few hours of running variants of previous missions, then promptly over.
EVE Online - I've badly wanted to love this game for years, but both times I made an earnest attempt to get into it, it just bored me to tears and I could barely make sense of what I was even supposed to do. Unless you're involved in the meta political stuff that everyone likes to report on from time to time, the game is just dull. Spreadsheets in space baby.
Ghost of Tsushima - Another "minor disappointment" as I actually liked playing it overall, but the game's open world is the epitome of style over substance. The most rote, perfunctory open-world content I've played this side of a Ubisoft title. By the time you siege the castle with Lord Shimura, I was just barreling through story missions and had completely lost interest in finding my six thousandth fox den or hot spring. A hollow open-world game with a really beautiful coat of Kurosawa-themed paint on top, fun sword combat, terrible stealth, and a story that starts boring but finishes strong. Not bad, but could've been so much more.
Sea of Thieves (at launch) - Was so hyped for this game - even bought the limited edition controller in anticipation - but it was just way too threadbare at launch. I bounced off of it within a few days due to boredom. It eventually grew into a great game I enjoy, but the disappointment from a lot of people was palpable at launch.