I have a huge head relative to my shaft (5.75-6 versus 5.25-5.5), and from talking with my partners, they really like the big head. I agree with the above - the girls can feel a big head even when it's deep in them, and really like/get off on that full feeling.
I also think that a big head can be as fulfilling as a thick cock. My shaft is bigger than average, but nothing to seriously turn heads (sorry for the pun). But most girls have said I'm the thickest they've been with, which I think is largely because my head is just really thick.
I also think women can feel thickness a lot more than length, especially with relatively small differences. For example, the last girl I was with said I was a little above average with a 7" cock, but she's only been with one or two guys as thick as me. Which I thought was strange, since a 7" is somewhere in the 90-odd percentile. But a 5.75 cock head made me one of the thickest she's had, and that's only what, an inch larger around than average?