Before I was cut, I was essentially unaware of the inner foreksin as a pleasure zone. I never rubbed it. It was just there to be over the head.
As semi cut, since my skin would automatically retract as soon as I started to get hard, I became more aware of it and would rub it gently during foreplay, but masturbated as uncut by moving skin up/down. However, on the downstroke, the inner foreksin would get stretched and that felt good.
Now that I am fully cut, my inner foreskin is tight when hard, and I can stimulate it more profoundly, rub it in many different ways and, as others have said, near the circumcision scar is more sensitive.
The bulbus part of head (ventral side) is very sensitive, as is the inner foreksin between the rim there and the scar (where frenulum used to be). That is exquisite to rub.
When I am still soft (for instance, just dropped underwear), just sliding my hand on on the top of penis will stimulate the inner foreksin, the rim of head and the dorsal side of head in a very very pleasant way.