Stormlight Archieve is his biggest series. He's going for 10 books, like 1000+ pages each, and broken into two main parts of 5 books each. It's epic as fuck, but you need to be ready for it.

And then because Sanderson is swinging for the grand slam rather than just a home run in terms of epicness, even that series loosely ties into his other series. For example 2-3 characters from Warbreaker eventually show up in Stormlight Archive, he has one character that shows up in almost all of his his Cosmere novels, and the overaching metaphysical plot involving the god-like shards affects all of his Cosmere worlds including Stormlight.

If I recommend his work, I usually recommend the Mistborn Trilogy first. If they like that, then onward to Stormlight Archive. If someone already likes Warbreaker that's a good start too. Warbreaker was one of his weaker ones imo.