Recently Karune posted a fairly large update and included in it some screenshots of Zerg units that have been updated recently with improved art.  Check them out below; they look much better than previously with additional detail in almost every aspect!

Quote from: Karune (Source)

Art Updates
The StarCraft art team have been making massive updates to the Zerg faction, adding various new animations and improving even further on the textures of Zerg units and buildings. A picture is a thousand words so check out the updates for yourself!

Baneling

Drone

Hydralisk

Overlord

Overseer