Looking at your shelf, the biggest gaps are in foundational fantasy that directly influenced the stuff you love:

A Wizard of Earthsea is the one I'd start with. Le Guin (you already have her sci-fi on your list) wrote the blueprint for the "magic school" story decades before Hogwarts, but it reads more like a fable than an epic. Spare, beautiful prose. Completely different texture from Sanderson but equally rewarding.

The Blade Itself is the antidote to noble-hero fantasy. Abercrombie writes characters who are deeply flawed and frequently terrible, but you can't stop reading. If Sanderson is the optimist's fantasy, this is the cynic's, and the craft is just as sharp.

Gardens of the Moon is the deep end. Malazan is what people mean when they say "epic" fantasy: ten books, hundreds of characters, zero hand-holding. It rewards the same patience you brought to Way of Kings, but the learning curve is steeper. Not for everyone, but the readers who click with it tend to rank it above everything else.

And if you're eyeing a really long commitment: Sanderson's Cosmere and Jordan's Wheel of Time are the two big ones. The Cosmere is modular (Mistborn, Stormlight, Warbreaker, each stands alone, connections are a bonus), so you can dip in and out. Wheel of Time is one continuous 14-book arc with famously slow middle books but a massive payoff, and Sanderson actually wrote the final three. If you love Way of Kings, the Cosmere is the natural next step. Save Wheel of Time for when you want to commit to one thing for a few months.

She's arguably stronger in sci-fi than fantasy, which is saying something:

The Dispossessed is her masterpiece. It follows a physicist who travels between two worlds with radically different political systems. It's a novel of ideas disguised as a story about one man, and the worldbuilding is as rigorous as anything on your shelf. If you liked the philosophical weight of Dune, this is its literary sibling.

The Left Hand of Darkness is what put her on the map. An envoy arrives on a planet where people have no fixed gender, and the whole book quietly dismantles how you think about identity and politics. It absolutely earns its reputation.