It's the worldbuilding, as much as the characters and plot, that make it good. The details Erikson came up with are what sets this apart from so many other epic fantasy books.

Fun fact, Erikson and his co-author Ian C. Esselemont created the world/setting a decade or two prior to writing any of the novels for their tabletop gaming. Initially a D&D game, it transitioned into GURPS and remained so. Various players at the table (including each author) played a great number of the characters we meet in the books. Which is another reason this series feels so good to read - these aren't just characters created for writing - they're characters who were played, which adds a depth of understanding to the characters that a lot of writers never reach.

I saw an original TTRPG map for the Siege of Pale back when I was following Erikson on Facebook closely several years ago, and it was super cool to see how a siege that appears later in the series (Siege of Capustan), is sort of inspired by the at-table events that we get as background details (Siege of Pale).

I could geek out about this series and its roots in TTRPG forever, so I'll stop before I write a bloody essay... but in case you wondered who played which characters, I've linked that below:

https://malazan.fandom.com/wiki/Role-playing_Game_Origins_of_the_Malazan_Series