If you have an appreciation for movies like Revolutionary Road or Leaving Las Vegas, you might like this movie.
I personally enjoy movies even if they are dark and leave some questions un-answered (Doubt is a perfect example of such a movie). I also enjoy a good character study, where a film is more about the complexities of humanity than a plot.
Rachel Getting Married is not some happy-go-lucky thrill ride with an ending that explains everything with a cherry on top. It is a character study. If you like character studies, watch this movie. If you don't, then don't watch this movie.