Nothing bugs me more about movies when someone says a movie sucks, but then they don't give any reasons for why they disliked it.
I would have to say the script, flow of the movie, shooting of the movie, acting/casting, and music of the movie are the most important to me.
Any movie can be the cardboard tale of two people meet, they fall in love, there is an obstacle, they make up, and then live happily ever after. But if you take that story and get strong actors and a clever script, it could get better. Then a great soundtrack, with the music connecting with the scene in just that perfect moment is great. I love when directions use different shots to show the story and it's not the same stuff you see over and over.