I liked Renarin before this book. I love him now, second fave behind Kal.
I really hope he can use Illumination as well as Progression, and also some other power manifestation from the corruption. That would be neat. Also, I don't think his moment with Adolin was Illumination, it seemed more like just Progression to me. And the thunderclast ultimate defeat could be related more to the corruption than to Illumination. As mentioned before, each order has more affinity for one surge than the other: Windrunners - Adhesion, Skybreakers - Gravity, Dustbringers - Division, Edgedancers - Abrasion, Truthwatchers - Progression, Lightweavers - Illumination, Elsecallers - Transformation (from Jasnah), Willshapers - Transportation (by logic), Stonewards - Cohesion (same) and Bondsmiths - Tension? (well, Dalinar has no problem with either, even though he begins by using adhesion), so as Shallan maybe we just have to wait a little to see him use it.