Trailers are a hit and miss nowadays...although it depends on which trailers one is talking about. One of the cool things about video releases before the internet became prominent was watching trailers of upcoming movies (and video releases) before the film itself began. Ditto for trailers seen in cinema...although in our movie theatre the trailers tend to be very loud, which diminishes the impact and tend to make them more annoying.

One of the worst offenders as far as trailers go is Disney whose American trailers rely too much on comedy and hectic action than actually telling us what the story's supposed to be about (or showing us the "heart" of the film, so to speak). Comparing the American and Japanese trailers of Tangled (or Frozen), for example, paints a totally different picture of the film(s) in question. Then again, Disney's marketing tends to suck more often than not, anyway, so it's just one part of a bigger problem on their end.