I broke mine before becoming sexually active... probably through sports, and probably before I was even aware that it existed. So I didn't notice.
I imagine that if it is broken during sex it hurts somewhat, I know that it often bleeds, but my guess would be that it is a momentary sensation of pain and then it passes quickly. I have never heard anyone refer to the experience as being pleasurable.
I don't recall breaking my hymen. I did bleed quite a bit my first several times have sex, but nothing had to sensation of anything 'breaking' You're too busy focusing on adjusting to a new sensation of something so large and different being innside of you.
If you break it during sex, it feels like you're trying to shove something into a hole that is too small to accommodate it, and it hurts. For me it continued to hurt the entire time we had sex, but it did hurt less and less as time went one. The sex was still pleasurable, though, it just had some hurty undertones. If that makes sense.
I was also kind of sore afterwards for a bit. It went away after a few days.
Boys and girls sexual organs are locked closed in childhood. In boys, the foreskin is literally fused with penis head, but slowly those bonds seperate. Same with girls, hymens thin out as you get older. Well its different for everyone, mostly because the the thickness and form of a girls hymen changes from person to person. Sometimes it covers the whole opening, but sometimes its just a few strands of tissue that are about the same size as a number of threads.
You should not worry about it too much. Most girls hymens are thinner rather then thicker. My girlfriend was like the other girls that responded here, they had hymens that were thin enough that at some point they just broke in regular activity.