It is a painful kind of pleasure for the other party-as long as it is consensus. But it sure does feel better because it is narrow and dimmer, it is like the equivalent of a very tight pussy. This is the hole is way tighter and harder to get into compared to a woman's vagina. During anal sex, usually, the dominant one inserts their hard penis with a lot of lubricant into the submissive one's asshole. As in gay sex, the best part is obviously the anal sex part-this is the counterpart of penetration for gay couples.
Sometimes the only best part in porn is the part of penetration-sometimes we are just too horny to care about the foreplay and the preparation of the whole sex.