There is a physical feeling and a psychological feeling in being bottom, in my experience. A lot of it depends on what leads up to actually having sex. The connection and attraction, the thrill of the hunt, the teasing and slow lowering of inhibitions. Of course kissing, petting are key too. Foreplay is important and a good top gets their bottom ready for them either with their mouth or fingers, saliva or lube - brining them to a point where they are panting and saying that they want it.
Then comes the penetration - that initial period when the bottom can feel the head of his lovers cock pressing to enter his body and the top taking the time to be gentle and slowly sliding himself inside. I think eye contact, caressing, kissing and all the rest adds to the eroticism and the psychological aspect of knowing that you have given yourselves to each other in the most personal and intimate way is extraordinary.
It's important for the bottom to reassure his top, telling him how big his cock is, how great his body feels, etc. If acceptable the bottom should let his top know whether he wants the cum inside him, in his mouth or on him. Of course if you know me you know where I put it ; )
Then after holding each other, caressing each other completes the perfection of being a bottom.