The four deaths within Act V certainly have a profound effect on the reader. Paris's death is almost welcomed by the reader. Although nothing more than a stock character, his presence at the tomb (and throughout the play, really) provides nothing more than yet another obstacle Romeo must overcome. His dispatching is rather uneventful.
Lady Montague's death is more shocking for it is one we did not see coming, announced almost coldly as though it is but an afterthought, It serves its purpose well, however, for emphasizing the tragedy the feud has brought about.
Of course, it is the deaths of Romeo and Juliet who have the most profound effect upon us. Not only are they they lead characters, but it is the nature of their deaths that move us. Their deaths are completely unnecessary (and in Romeo's case, completely misguided), but they also both commit suicide for the other with love being among the last words upon their lips.
I would say that there is a certain level of loss that is even felt by the reader at the end of the play. Similar to plays like Macbeth or King Lear, the mortally destructive aspect that concludes the Shakespearean Drama brings a great level of gravity to what was experienced. It allows us to contrast what was felt at different parts of the play to its finality, an ending where redemption is not going to be experienced by the main characters, but can only rest with some of the side characters and the audience, in general. Contrast the end of the play to some of lines spoken between the two lovers that speak to the level of "love" or infatuation that is experienced. Contrast the dreams and plans of each and those who supported them to the ending. The conclusion of the act with the presence of multiple deaths reflect the large gap between promises and realities, of what can be as opposed to what is.
A Shakepearean tragedy conveys the sense that human beings are doomed by their own errors or natures, or even an ironic twist of their virtues, or through the nature of fate or the human condition to suffer, fail, and die. In Shakespearean tragedy, the hero usually dies as a result of his tragic flaw, moral weakness, or inability to cope with unfavorable circumstances.
One common weakness that many characters share in Shakespeare's Romeo and Juliet is impetuousness. And, as a result of their impulsive personalities, accompanied by the unfortunate circumstances of fate, Mercutio, Romeo, and Juliet all die.
For these tragic deaths in Romeo and Juliet the reader is well prepared. First of all, the Prologue to Act One mentions that fate has a hand in the tragedy--"the star-crossed lovers"--and the enmity between the Capulets and Montagues breaks "to new mutiny." The first scene opens with strife and renewed hatred. When Romeo falls in love with the child of his family's mortal enemy, there is certain foreboding of a tragic end for the lovers. Certain speeches foreshadow the tragic ending as well. For instance, when Friar Laurence cautions Romeo, saying,"These violent delights have violent ends"(II,vi,10), and Juliet declares, "My only love sprung from my only hate" (I,v,133), there is foreshadowing of Romeo and Juliet's doom since they are too quick in their love too swift in their actions, and circumstances work against their marriage.
Then, when Friar Laurence and Juliet plan her feigned death so the parents will be so relieved to have her alive that they will not be too upset with Romeo, whom she has already married, and the message that Juliet lives does not reach Romeo in time, fate's hand enters the play. The tragic delay to Romeo's knowing Juliet is really alive, coupled with his cries of "O, I am fortune's fool!" prepares the reader for the unfortunate results, results that still bring a poignancy to the audience. For, the beauty of such young, romantic lovers is what dreams are made of, not tragedies.