I don't know that I have any words to this point specifically, but I wanted to share my experiences as a relationship-positive, highly sensual, sex-neutral ace for comparison with some of the more allosexual members of the forum.
I've only ever had sex with people I've had very strong feelings for - to me it's a very intimate act. That said, my actual feelings during the act are... strange. The lead-up, cuddling, kissing, messing around are all enjoyable. I'll also end up with an erection as often as not along with a generalised, but not strong, urge to have sex. If I do follow through with that, then it... happens.
And this is the bit that's always stumped me, listening to other people. I've never felt pleasure from sex. Not physical pleasure, nor emotional pleasure. I've done it because it's expected and it's not bad, but I've not really had a good experience during the act. Before and after are often lovely though.