It's not a binary choice between enjoying everything completely or not at all. I have a preference. When that preference is not met, I would enjoy something less than if it is met, even if everything else is the greatest thing ever. That's all there is to it.
Personal opinion: what I consider "spoiler" is the obliteration of tension. Tension is the lingering question of "how". Right from the beginning, two people with clashing views, glaring at each other. Thus the question is born. Not "what", because we all know what would happen. They fight, they break up, they kiss, they make up, yadda-yadda-yadda. But rather, "how". "How the heck are Batman and Superman going to reconcile?"
Then suddenly the trailer answered that question. It abruptly replaced the tension built through the entire first trailer and the 2/3 of the second one with "How would Batman, Superman and Wonder Woman beat Doomsday?"
The Avengers trailers never presented its tension in such a way. From the very beginning till the end, its "how" is a simple "How would the Avengers defeat the alien invasion?"