The title of William Shakespeare's The Most Excellent and Lamentable Tragedy of Romeo and Juliet (which is now more commonly referred to simply as Romeo and Juliet) tells us a few things about the play we are about to read or see.

The use of "Most Excellent" in the title refers to the quality of the written material and/or the production itself rather than the particular events of the play; in fact, the narrative of the play is hardly an "excellent" story in the "feel good" sense, as we learn in the next part of the title that this is a "Lamentable Tragedy." In other words, we are about to watch some very unfortunate circumstances unfold, which will most likely end in death, as most tragedies do. Because the only two characters referenced in the title are Romeo (a male) and Juliet (a female), we can deduce that they are the protagonists of this tale; contemporary cultural knowledge of these names might also suggest to us that the pair are lovers.

Thus, we are prepared to see a play with high production value in which a sad series of events results in the deaths of the story's central figures. 

The full title of Shakespeare's famous love story is The Most Excellent and Lamentable Tragedy of Romeo and Juliet. A tragedy in a general sense means that things end badly; a tragedy in drama means that things end badly (usually in death, or multiple deaths), and, usually, that the terrible ending arises naturally from flaws or weaknesses in the specific characters, especially in the specific situation in which they find themselves. Therefore, we know that this play will end in sadness and likely with the two main characters dead, and that the deaths will come from who they are. In this case, the deaths come from the intensity of their desire, the fact that they come from warring houses, and that they are so young, all combined.
Greg