Have to say, i don`t watch too many trailers, but i do agree that some show too much and often for too long. What i have found a few times, is that the trailer can sometimes be better than the whole movie, a good example of this, for me, was the trailer for `The Creator`. I  watched the trailer for this film and sat there eyes wide thinking, `i cannot wait to see this`, but for some reason, was left a little disappointed after seeing the movie, it didn`t give me what the trailer did and i have no idea why 🙂

Very often a film is `sold` to me by who is in it and who directs it, generally that`s enough for me.