City of Blades is the perfect sequel - it draws on what happened in the former, continues the overall arc and concerns of the series, but it never retreads the ground broken in the first book, preferring instead to do new and interesting things.
I think this series, along with Gladstone's Craft Sequence, showcase just how versatile epic fantasy can be. Both series take epic fantasy into almost contemporary settings and then play out the battles on those stages and it works so well.