It's not about "knocking points off a score". The score doesn't really matter. It's a sense of "I've played 3, 4, 7 times already (looking at you, Assassin's Creed)". Ideally, a sequel expands upon and evolves the foundation of its predecessor; in some franchises, more of the same is fine, since adding more would ruin the fine balance of the concept, but in general, sequels try to build on what came before. That criticism of feeling like you've experienced it all before, to the detriment of the work, is a criticism of design and structure. It's part of why some movies, games, books, etc are able to subvert and twist expectations