Ubisoft created AWESOME games like Assassin's Creed IV: Black Flag, Rayman, and Watch Dogs, but Uplay, albeit great, it's servers and internet suck, and it's a hassle to get it working.
When a game just becomes so ridden with flaws that it's just simply no longer able to be enjoyed. This can apply to games that are just ridden with bad battle systems, petty annoyances that occur frequently, or other quirks.
Final Fantasy VI, on the PlayStation Final Fantasy Anthology version, is unplayable due to horrid lagtimes for menu screens, battle, towns, and encounters.