Yeah, Sculptris is awesome, and it's free (at least for now). I find it much better than sculpting in ZBrush, you work faster and there is much less hassle. And you can always switch directly to ZBrush and back for those special tools which Sculptris lacks, like punching holes in your models or hard surface sculpting.
Although if you want to retopo, you need to do it by hand in another tool, like ZBrush, or any 3D package (there are many techniques). Personally I use a great tool called 3D Coat, which has a pretty robust automatic retopology feature, then just fix the trouble areas on the mesh in Softimage. That way I can have a game ready model which would normally take a few days of work in an hour or so. Very efficient workflow.