Very Good Software
I think the product speaks for itself in terms of the stunning results that come out of it. Superb organic modeling software. I've compared ZBrush to Autodesk Mudbox and in general I like the interface of Mudbox better (more intuitive), but ZBrush is a more powerful/practical/less expensive tool. And has much better performance in my opinion. Mudbox slows to a snails pace after only a few subdivisions, at least with my limited experience on my computer. ZBrush seems very well optimized to handle very high resultion meshes, and has modeling features that Mudbox does not. Still though, if you're new to both, it is worth trying out the free demos of each tool to see which one suits you better. I did, and it's ZBrush for me!