In a nutshell Zbrush is a very dense forest, filled with very clever tools but often implemented in a clunky way.
This along with countless procedures, settings, exceptions, prerequisites, etc.

If you manage sift out only the things you need and don't bother with all the rest of the stuff it's not so bad, but still not very easy at first.
No doubt that for organic modeling it's quite powerful.

Don't know much about 3dcoat though...

Marc