It is definitely true that there are many parts of this complicated requirement, and it is beyond my capabilities (and time) right now to provide a full explanation of this Mitzvah. However, I will quote some relevant passages from Rav Eliever Melamed that attempt to explain this Mitzvah. A good read on this topic is his Sefer Simchas Habayis Ubirchaso, where the quotes below are taken from. At that link, I would suggest that one reads at the very least, sections 2 and 3, which discuss the Halachic requirements of Onah, and the definition/meaning of the word Onah.
I am specifically adding this answer to provide sources that show that a man should ejaculate and woman should be brought to climax as part of this Mitzvah, and that they are possibly requirements of it. He states these 2 requirements explicitly below (Section 2 in the above link)
מצוות עונה היא שיתייחד האיש עם אשתו באהבה ושמחה יתירה, ויענג אותה ככל יכולתו עד שתגיע לשיא השמחה, ויתייחד עימה בייחוד גמור עד שזרעו יצא לתוכה באותו מקום שבו היא יכולה להתעבר (להלן ב, א).
These components of the Mitzvah do fit in well with his further explanations and Halachos, again, I would forward any interested reader to the above link, where it is explained in more detail. It is possible that not fulfilling one of them does not "invalidate" the Mitzvah, but certainly seems to be a requirement Lechatchila.