The male g-spot, also called the p-spot which stands for prostate, is a walnut shaped object that one can feel upon enterinig the asshole and pushing up. One can stimulate it with fingers, a butt plug, a dildo, or even vvarious vibrating devices.
It is a type of orgasm that physically (almost) every man is able to have, although many choose not to. The subjective feeling is that it is a strong pulse through the entire hips, and their entirety is grasped by the sensation. The vibrations flow strongly forward and out. It feels not necessarily better, but dfferent, deeper in a way, but less concentrated in pleasure.
In general I haven’t heard much about people having multiples, or several in succession of these, although perhaps it is possible.
Just as with anything, variation in enjoyment of stimulation and ease of orgasm happens.
Unlike a penile orgasm, the semen floods and dribbles out rather than shoots out.
In one book on tantra I read, an argument was made that men who had G-spot orgasms have a looser pelvis in general and thus have more dick control. The theory makes sense.
I had a correspondence with a sexologist discussing them (I’m sorry, I forget the name). From what I remember: they are distinct from penile orgasms in having the brain deliver the message to release on the vagus nerve as opposed to the sympathetic nervous system. As a result, though, tantric techniques of pausing an impending orgasm are not effective.
This, the standard penile orgasm, and, arguably, multiples (see Male Multiple Orgasms? ) are the only orgasms men have.