So in my opinion there are two ways to answer your question:
1. What do most people think are good pokemon games that are worth playing?
2. What Pokémon game is worth playing for you?
Basically, from what I've observed, fans seem to love the following games(in no particular order): Heartgold and Soul Silver, Platinum, Black and White 2(some love Black and White, but their sequels seem preferred), Emerald, and Crystal. It seems the newer games(Gen 6-8, though SwSh seems overwhelmingly positive so far) get more mixed reviews, but that is just my observation. Maybe opinions are just stronger about them right now because they are newer.
Now that being said, what matters most is your experience and enjoyment with it. There is just something special about playing your first Pokémon game that is hard to explain. My first game was yellow, but then I got gold and just fell in love with Johto, so my all time faves are heart gold and soul silver as perfected versions of the gen 2 games I grew up with and love. I also LOVE Unova because it got me back into Pokémon within the last few years, so it kinda holds a special place in my heart now.
So go ahead and enjoy the crap out of Moon. You will prob compare other Pokémon games against it and have fond memories attached to it, and that's great! Personally, I'd recommend HG/SS and The gen 5 games, but that's because I enjoy them the most for the reasons mentioned above. So that gives you plenty to work with, but at the end of the day, I'd say enjoy moon and then see where your heart leads you from there. :)