Thanks Bjorn and Bill. Your comments are much appreciated.
Playing it in the car yesterday I thought "where's the bass!". That'll teach me for rushing it out.
I have been using iZotope Tonal Balance lately to help identify any deficiencies but somehow missed it out when I put this track together. Must add it to my default template.
I was going for quite an extreme vocal sound; loud but with a whispery/hissy edge if that makes sense. I will try adding the lower mids in the vocals though.