* It is surprisingly small
* It is kinda "fuzzy" or "blurry", you can't detect too much brushwork.
* It is very expressive
But my favorite Vermeer is not this, it is View of Delft, also in the Mauritshuis. The colors, hues and textures on it are just amazing.
For Brazilians, a funny curiosity: Mauritshuis means House of Maurice. It is really the former residence of Maurice of Nassau (Maurício de Nassau), the governor of the Dutch colonies in Brazil. This museum also have some interesting works by Rugendas and other painters showing life in colonial Brazil and a very cool collection of puppets made with bread paste showing life in colonial Indonesia.
The Mauritshuis is a very good reason to visit The Hague. If you go there take a walk to the M.C. Escher museum too.