Shields now come in three sizes, in every metal. Ferris and the other smiths sell them, and you can forge and upgrade each one.
Round: light and quick. You barely slow down with it raised and still hit hard behind it, but it stops less and covers a narrower arc.
Kite: the all-rounder, just like shields until now.
Tower: a wall. It stops the most, covers the widest arc and has the biggest guard bar, but you move slowly and hit softly while it is up, and its guard bar is slower to refill.
A shield's size is the shape you see. Shields you already own keep their look, so a round shield is now a round shield and a tower shield a tower.