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If you’re looking for something less childish (or not YA) and less bigoted, I would suggest not thinking just in terms of series, but in terms of prolific authors.
People have mentioned the Discworld series, which is a series in the loosest sense of the word. They occur in the same universe and the books share characters. There’s individual storylines with min the series as well (eg the Witches books). You can start pretty much anywhere because each of the books is self-contained, and when you do stumble across, for example, the origin story of a character you liked from a novel where they were appearing as a costar, it’s always a bit more fun than if you had worried about getting all the backstories down in the first place.
I’d also recommend Neil Gaiman. His works are even less collected than Discworld, but there are commonalities and shared mythologies that make them feel coherent. Good Omens is where I’d start - it’s a feel good rom com about the antichrist and the end of the world. American Gods. Graveyard Book. The Sandman series is pretty brilliant both as a graphic novel and as a full-production audiobook. He has a ton of other work, too.
Neal Stephenson’s Baroque Trilogy is a compelling piece of pretty accurate historical fiction incorporating the great figures and events in science and politics of the 18th century (Newton, Leibniz, Hanover, the English civil war, Hooke, cryptography, natural philosophy, puritanism, capitalism, and so on). In total it runs a bit over 2000 pages. It’s not high fantasy though. It’s more like historical (science?) fiction.