The ones I can think of right now:
Dragon Age Origins: great RPG full of possibilities and roleplaying choices, with a gameplay that was essentially KOTOR in a medieval fantasy. Then came DA2 which was way inferior, and then Inquisition, although an improvement over 2, it just didn't reach the standards set by the original game.
The DA series worked better as an old-school RPG IMHO. It suited that world, it's the kind of which benefits the most from a traditional RPG style, not as an action RPG.
Horizon Zero Dawn: I don't hate the sequel (I like it quite a bit in fact), it just doesn't make me feel what ZD did: a Hero's Journey from beginning to end, Aloy's journey from outcast hated by her tribe to a hero who feels insulted when worshiped by the very same people due to the very same absurd prejudice. It was a story about finding out what happened to the world and the people who had a hand in both the world's demise and its salvation, and how their actions still echo long after heir deaths, affecting the current world.
The sequel just didn't have that awesome feel of wonder the original had, so for me it's nowhere near as memorable.
Dead Space: seriously, this one didn't really need sequels, the first game was pretty perfect, it felt like a film. The score, the atmosphere... all amazingly done. One of the most memorable games I've played and a true Sci-Fi horror classic.
The second one was fine, but it didn't reach the quality of the original. And the third, while it expanded the lore in interesting ways, made the mistake of ditching the horror in favor of the action, which worked against it.