  Let E be a product system of C*-correspondences over N^r. Some sufficient
conditions for the existence of a not necessarily regular isometric dilation of
a completely contractive representation of E are established and difference
between regular and *-regular dilations discussed. It is in particular shown
that a minimal isometric dilation is *-regular if and only if it is doubly
commuting. The case of product systems associated with higher-rank graphs is
analysed in detail.
