Dunno why people are putting such a high premium on their presumed reaction to Doomsday's introduction in the film.
"They put Doomsday in the trailer!"
"So?"
"So it could have been a surprise!"
"Would you really have been surprised?"
"Yes!"
"No you wouldn't. The film is going to make it super-fucking-clear long before it happens that Doomsday is coming."
"But now I'm not surprised at all"
"You were never going to be surprised. This isn't a surprise. It's not meant to be."
I'm pretty pissed that they have shown Batman and Superman fighting in the trailers.
Imagine the surprise to the audience during the movie.