its a nice head model for a starter in zbrush but some problems with it like
[1] the temble of the head is too inwerds
the lips look like he is smileing
the male face has to be more bulking the nose has to have alot more bulk
check this out it might help you
http://www.zbrushcentral.com/showthread.php?t=159772
this is a head model i maed useing just a ball