I played for awhile on launch after dropping off shadowlands HARD. I've been playing on and off since BC.
It's okay, probably my favorite expansion since pandaria. The first raid was pretty fun on heroic but still felt a little shallow compared to the classic cadre of raids (ICC, Ulduar, Sunwell). The mythics felt pretty well designed apart from some really iffy affixes for the first season, I dropped out before the new rotation so I can't attest to that.
Overall the game just feels way too grindy for me to get into anymore. Professions still feel useless and I don't get satisfaction out of pushing m+ to see my rating go up. It was wayyy better than shadowlands and BfA in my opinion, and if you have a good friendgroup / guild to do content with then it's a fun time.
Pushing m+ raiting lost its appeal for me when I realized how widespread paid gold carries are. The majority of people with good enough raiting that you'd want to party with barely know their class rotation. Raider.io is basically completely bullshit outside of the very top guilds and m+ teams in the world who earned it legitimately.