The Spectacular Now - It left a lot to the imagination. I thought the movie would be really fast-paced and truly shows what it's life to fall in love for the first time. The trailer was sad and uplifting at the same time. The movie itself turned out to be really slow. And rather than showing what your first love is like, it showed what your first relationship is like, one where you think you're in love, when really you're just 17 and want to know what love feels like. Which in a sense, was more realistic. But yeah, the trailer was way better than the actual movie.
The Impossible - the music and editing in this trailer were so good they made me cry. The movie's still great, but it's a really powerful trailer.
The Fault In Our Stars - This trailer also made me cry. I'd been waiting for this movie for ages, and the book also made me cry. But just seeing Shailene Woodley crying in the trailer made me realise how good the performances were going to be. This trailer was full of feels Especially the "I am in love with you" scene at dinner, where she cries. And then again at the eulogy when she says "you gave me a forever with a limited number of days, and I can't tell you how thankful I am, for our little infinity" It also annoys me that they used different takes in the final film, because the ones shown in the trailer were so much more powerful, even if she was a little bit more difficult to understand.
Especially the "I am in love with you" scene at dinner, where she cries. And then again at the eulogy when she says "you gave me a forever with a limited number of days, and I can't tell you how thankful I am, for our little infinity" 
It also annoys me that they used different takes in the final film, because the ones shown in the trailer were so much more powerful, even if she was a little bit more difficult to understand.