Those who have answered this question before me have grasped the gyst of V.W.'s purpose perfectly, so it'd be redundant to harp on what has already been said. Still, there is still the factor of experimental writing in which she and some of her contemporaries were involved, and the extraordinary resource of highlighting the passing of time through the description of the house in Part II. It's thought-provoking that humans play practically no part in this section of the novel, and that the three deaths are mentioned in passing, as it were. To my mind, the symbolic meaning of the house decaying only to come back to life in anticipation of Part III is an amazing literary resource, considering the time when the novel was written. One last thing that I'd like to mention is the poetic quality of the prose, a feature very much her own, since other contemporary writers of the stream-of-consciousness (Joyce and Faulkner, for instance) did use language features in new ways, but did not seem to find the poetic element important to their constructs.  

In terms of style, it seems as though Woolf was attempting to capture the fleeting, elusive nature of reality through the use of multiple perspectives.  It would be difficult to describe any one of the characters in a few words because there is a wealth of information concerning each, from their own thoughts to the thoughts and feelings of others.  It is necessary for the narrative to be fragmented because that is how real life is. The key to understanding human life can not be found in a linear fashion. Life is chaos, and Woolf's competing narratives are her way of bringing structure and form to this chaos.

One of the most important things to remember while reading To the Lighthouse is that this is a Modernist novel. Yes, stream-of-consciousness is very important to the structure of the novel because it puts the reader in the minds of the various characters and very much in the moment of the novel. But the style of the novel is important well beyond stream-of-consciousness.

For instance time and plot are skewed in the novel. The reader gets a sense of Personal time which is subjective and privileged to each character. The novel also feels dream-like at times, makiong time very difficult to sense at all. Characterization in the novel is fragmented, fluid, elusive, irreducible, and indefinite. We are given a circular and subjective narrative that can be difficult to follow, but also wonderful!

"To the Light House" is a wonderful novel. Stylistically, the thing that is most unique about it, I suppose, is her choice to do stream of Conscious narrative. Woolf, and of course, James Joyce, are most known for this narrative. Stream of consciousness follows the voice in someone's head as they are thinking it. In this novel, Woolf does this with a myriad of characters. Making it, if you're not careful, a little difficult to follow.