Diablo 3 is a Diablo series game.
Play what you want to play?
I own them all, and also Project Diablo 2, and I rotate through them all when I'm in a nostalgic mood for D2 dopamine hit on rune drops or want to play current Season 7 of D4.
Diablo 3 is a filler for me, just play for funsies, make a build that can blast through GRifts and Bounties and you'll be fine.
If you never played before, just play through the story once for lore purposes.
After that, every end-game in every diablo is the same... Grind for better items and optimize your build til your eyes bleed and you stop playing it.