People tended to like the Assassin's Creed DLCs but I played two and thought they were both dogshit.
Freedom's Cry especially had this fever pitch of critical acclaim for being about woke mandingos killing slavers, but it was hot garbage. Instead of playing in new mechanics to its Haitian maroon setting, maybe making a focus on navigating dense jungles or blending in socially with disguises in a complex society, or anything, it just was more Black Flag but with a big shotgun. But moreover, the Black Flag formula doesn't work in that setting. The ships work well when you have vast areas to explore, the ability to actually voyage from place to place, find stuff along the way. I thought when it was annoucned that we were getting the whole small islands part of the Caribbean that was cut off of Black Flag, but it was just the little bay around Haiti. That's it. That's like sailing a remote controlled boat in a toilet bowel. Moreover, people praised it to high heaven for how it relentlessly revealed the horrors of slavery through its little side missions, but I found that they came so ridiculously often that it lost all realism and became absurd.
Dead Kings had a similar issue. It was pitched as being the dArKeSt Ac YeT, set in the necropolis of the French kings with (Animus-related) ghosts. That could have been a very interesting thing, try to play off AC as a horror game. But the gameplay instead turned out to be the same shit but in cramped tunnels that weren't suitable for it, and the tone was laughable, it was actually the goofiest of all of them, you have a literal child sidekick. It sucked.
Unpopular because I remember a lot of people making a big deal out of how good they were (comparing them favorably to their main games!).