It’s hard to make sequels. Adding more of the original game can make the formula stale - the sequel will feel more like DLC. Making something entirely new may alienate the original audience, and you may lose the core of what made your game fun. Even making something new-ish, with several core concepts maintained, can fall short of the original if your audience’s tastes have shifted over time. Plus, the novelty or surprise of the first playthrough is often a significant portion of a game’s enjoyment - an advantage that direct sequels won’t have.
Therefore, it’s pretty common for a sequel or expansion to not top the original game. It just happens. But also… I think that’s okay.
I see sequel frenzy most often in the game industry - the assumption that each new thing will top that which goes before. And personally I blame boring videogame marketing tactics like MORE BULLET. IMPROVED AI. SOFTER DOG… which understandably has instilled in players a mood that they’ll have even MORE fun with this new game than the original. A formula for disappointment, I think.
Yes, sequels can be worse. Expansions and seasons, in particular, are probably going to fall short of the original experience. But that doesn’t mean the game itself is necessarily awful. It may even be excellent, the second-best game you’ve ever played. It it just may not better than the original. It may just miss a few of the notes that hooked you in the first place.
I think what kills sequels is often that expectation of strict improvement, that pervasive tinge of comparison. It’s not our fault as players that we have this expectation in the first place, but if we can set it aside and appreciate what’s in front of us in the moment, it can help make the latest experience still feel meaningful on its own merits.