I tried versions of the main characters that were less cartoony, and also ones where they were in geniune naturalistic portrait form.  Both were frightening for the most part.  Quill's was the first done, and is an exception.  It seemed to work because I first drew the younger version,  then altered it.  The young version is incorrect, though--Quill's hair had that odd style from a young age.  You can blame it on a 3 year old's sense of style.  Of course, once I drew this and saw what it looked like, my style started leaning that way...