When the ZBrush model is signed off on, our characters are around 40 million polygons. Some characters actually exceed that number even further. The number does not say anything about how detailed a character is, but it definitely says something about ZBrush; namely that the software maintains its ease of use when working with such high-resolution models. I am sure many artists used to other applications know how frustrating it can be when your software is not responsive enough.
The target polycount for our in-game characters is 10,000 triangles. For characters carrying large and/or complexly shaped accessories, we can use an extra 2,000. Human heads have a separate budget of around 4,500 polygons. We remesh the ZBrush model in a dedicated piece of software which we also use for generating our detail maps. This can only be done by decimating the model first - so thank God for Decimation Master! This plug-in does an outstanding job. When we finish our new topology we then have to create a UV layout before generating the normal map and ambient occlusion map.