Not sure if this was ever answered, so I'm going to wade in--sink my teeth into the subject, as it were ;-)
First off, much depends upon whether or not the penis in question is fully erect--a fully erect penis is likely to take more damage as it loses its "roll with it" capacity, i.e., that wonderful roley-poley quality that helps to prevent both puncture and crushing wounds. A fully erect penis is also possessed of a fairly impressive blood capacity via the corpus cavernosa, making a severe bite a far more bloody affair with erection.
Placement of bite is also important--assuming the penis is erect, severing of either of the two dorsal arteries would result in an impressive spray of bright red blood, whereas severing of the dorsal vein would result in a slower, pulsing bleed of a darker color. Any of these could result in death if steps to stem the flow of blood are not taken immediately.
Placement of the penis in the biter's mouth is also very important--incisors will sever blood vessels and cut through the corpus cavernosa, whereas molars will result in crushing injuries which are less likely to lead to severe hemorrhage. Presence or absence of foreskin would also make a difference in bleeding, as well as affecting the biter's ability to grind into the shaft proper.
While I can't say with authority how much control the man being bitten would retain, I think it's safe to say that reason would flee in short order. Likely the worst response would be to attempt to knee the biter--a knee to the jaw and a bad bite becomes an amputation. Sharp blows to the temple of the biter, thumbs ground hard into the biter's jaw, or fingers/thumbs to the eyes of the biter would probably inspire him/her to relax the bite. I wouldn't be surprised to hear of a man losing bladder control or rectal tone in the face of a severe bite, nor would I blink at the idea of a man swooning, or even losing consciousness from the pain or shock. Obviously, any bite that breaks skin would require medical attention ASAP.
As for what the biter would experience? Assuming an erect penis, think uncooked octopus meets turkey neck. A real sinewy feel, not easy to bite through--it would take a good amount of side to side motion in addition to clenching down--think of the way horses chew. If a blood vessel is severed or one of the corpus cavernosa layed open, there would be a LOT of blood in the mouth.
Hope that helps.
<big, toothy grin>
Kallie