Warhammer, both Fantasy/AoS and 40k, have a billion books so if that’s what you want, I’d say definitely check out at least a couple of the different series. Horus Heresy was mentioned, then there’s a different series about Egyptian space terminators that is highly recommended, think the book is called Infinite and the Divine, then there’s all the Ciaphas Cain books, really there is an ungodly amount, and all of that is just 40k.
On the Fantasy side, most highly regarded is probably Gotrek and Felix, a guy and a dwarf that travel and kill monsters and shit.
There are a shit ton of series to choose from, you could easily spend a long time reading only Black Library if that’s what you’d like.