Wheel of Time was my favorite series, until Stormlight Archive.
He does characters quite well. The dialogue isn’t always there, especially if the character is supposed to have a clever wit like Mat, but he’s getting better at that, too, with practice. But in terms of depth of character and setting he’s pretty fantastic. His characters are flawed and relatable and feel real, wound very well into his mastery of story structure. In Wheel of Time Androl is an excellent example, as that character was almost entirely Sanderson’s.
I recommend starting with either The Final Empire (first book in the Mistborn series) or The Way of Kings (first in the Stormlight series). The series eventually begin to intertwine and crossover to one another in a really brilliant way.
Bela was absolutely flawless.
I think Sanderson would be the first person to admit he didn’t do Mat justice. He’s spoken before about how difficult it was to write Mat.
Definitely give him a shot as an author. I think he’s brilliant, and he has SO. MANY. BOOKS. 😁