The physical and mental/emotional sensations of being fucked are a wild ride for me!
Physically, man it can be painful at first if not totally relaxed. But assuming the Top takes his time and you're both well lubed...then the pressing of his cock against your ass is so exciting, the pressure builds until the tension between his spongey tip and your tight ass gives way and you feel this gradual opening up. It's not that that feels good, not yet...but psychologically it really revs me up - my bi side is purely sexual, and I'm totally bottom/sub and I kind of feel less masculine and humiliated at being fucked. So that first moment of penetration breaks any illusioms, and firmly defines his Alpha/my beta.
The next minutes are literally breathtaking, as he works his way deeper and pushes past inhibitions. I tend to get with only very well endowed guys, and you just forget how all enveloping the feeling of a big cock is until you're taking it again. You can literally thinkmof nothing else but accommodating him. My ass does usually, slowly adapt to his girth, but length is trickier. As he's getting deep, it gets pretty sensitive and I can literally feel him pushing my organs aside. It's kinda uncomfortable to be honest, and needs to be done so slowly and carefully at first. But it does start to feel very good...
Finally, the feeling of his balls against my thighs or my own, priceless!
If we're all good to this stage, then the fucking itself is much easier and more enjoyable. The best position, speed, angle and depth depends on a lot of things, and if you're not synching then it can be unpleasant to be honest. But if you are, all those variables can combine into an incredible toe-curling, sheet-scrunching, mind-bending experience. If you've ever wondered why women moan when they're fucked but men doing the fucking don't, then you need to take a fucking...I had no idea I'd moan, but with the right guy I don't even know I'm doing it.
That's what it feels like to me, being fucked by a cock.