One of the biggest subjects is the Happily Ever After. Why oh why cry some people does Romance have to have a Happily Ever After? I have gone over this before -- basically it has to do with the commercial nature of the genre and the need for an arch plot type structure..
However, I want to add a further requirement,and maybe this will make the why oh why brigade happier.
I have been thinking about this because of Swain.
Any good fiction must have a satisfying end. It is when the pent up tension is released. If the tension is released to early and all that the books has going for it is the tying up of the external conflict, it feels flat. If it isn't released, the reader will feel cheated.
In a Romance, the reader should feel that the only emotionally satisfying ending is the HEA. They can stop holding their breath, these two people will get together.
If a writer writes a HEA but there is no release of tension, no culmination of fear, the reader is going to feel cheated. The ending has to be emotionally satisfying as well as happy.
The reason readers read is the tension. In the case of a romance -- romantic tension between the couple. It is why I read, it is why books are popular. But where there is tension, there must be resolution or the reader will be left feeling unsatisfied.