The saying goes that across most creative outlets, "the original is the best". Early musicians are often at their most passionate; authors have the most essential thoughts to put on the page, but in video games, we have a medium of iteration.
It is SUPER rare that when you have game mechanics perfected over time or scores of developers becoming more proficient with technology - that subsequent instalments aren't fundamentally better in every respect.
Those anomalies do exist though, and often there's just no way to recreate that powerful original spark that birthed a fanbase in the first place.
Over time it's common for long-running IP to mine every remaining aspect of what went down well before, just to try and keep going.