It really depends on the guy and how experienced he is. Using a straight analogy: when a man is performing cunnilingus he is getting his partner warmed up and horny. He can use a combination of his mouth and his fingers to get her worked up and he knows when she is ready. When he enters her it's a relief that he pussy is getting the attention it deserves. But he has to be a good and patient lover.
Same with M/M sex. The bottom has to want to receive his lovers cock, but (as others have said above) that's not so easy. The top has to take his time and, like with a woman, get the bottom's anus ready and willing to be penetrated. This he can do with his mouth, his fingers and - often times - lube. Unlike with a woman, where the vaginal opening is much more pliant, the bottom's anus is usually tight and requires slower progress starting with one finger then, when he's ready, moving on to the next and so on until the hole is sufficiently stretched, lubricated and the bottom is indicating (verbally or physically) that he wants/needs to get fucked. The top then adds lube to his dick and slowly enters his lover.
What does it feel like during that initial penetration? Think of it as the feeling you get when you have an itch and you get it scratched. Pleasure and relief rolled into one. As the cock goes in and out the walls of the bottom's rectum surround it and massage it. The head of the cock will rub up against the prostate to stimulate the bottom even more. Does it hurt? Yes, but in a good way, but as the fucking continues the top's cock will become harder and harder and stretch the hole more and more.
Personally when I have topped the best orgasm for me was inside my lover - I felt like every drop of my sperm was drawn out by his body and I was completely sexually satisfied. As a bottom the orgasm during/after being fucked is mind-blowing. All that stimulation (which may have lead to a heavy flow of pre-cum) usually results in an intense release sometimes accompanied by anal orgasms.
Days later the bottom can do anal contractions and still feel that cock in him. It's the gift that keeps on giving. My apologies if this is too long.