For me NTR is like sexual food.
Low quality NTR is fast food. It's for when you're feeling horny and just want a quick fap. In that case, it's best if the story is short and the scenes hot. The characters of the cuckold, cuckoldress and the bull don't matter, just their physical attributes. Most times the NTR occurs because the bull has a bigger dick than the cuckold and/or is just better at sex than the cuckold. The female character only needs to look attractive.
Medium quality NTR is homecooked food. It is not the best food but it's still quite good and filling. The characters of the cuckold, cuckoldress and the bull do need to be defined slightly and the story should be fast paced. Often times, the NTR occurs because the bull schemes against the female character. Usually the scheme involves blackmail, drugs, alcohol etc. The main point is to spend some effort on the characters to enrich the story and give the sex scenes more meaning.
High quality NTR is food from a 5 star restaurant. The NTR needs time to simmer. First, the relationship between the cuckold and the cuckoldress is built up over time. Then, that bond is severed by the bull and the relationship between the cuckoldress and the bull is built up instead. To make the story effective, their characters need to be strongly defined along with their physical attributes. It's best if the cuckoldress is a high quality woman. She should be loving, loyal and lovely. But the story needs to justify her choosing the bull anyway despite her intent to remain loyal to the cuckold. The bull should seduce her and prove that only he can take of her emotional and sexual needs. Ultimately, the story should end in tragedy for the cuckold while the cuckoldress falls for and is impregnated by the bull. I find that high quality NTR stories are deeply emotional and memorable.