• The Lady stands for art.  The atmosphere surrounding the Lady's tower appears pleasing in nature.  The isle "imbowers" the Lady, literally meaning to surround her with foliage.  The reapers appreciate art, her song, but those involved in commerce below (heavy barges, slow horses) do not notice her.
• To me this poem speaks out against living in isolation.  Yes, at first she doesn't mind living in isolation, but then she begins to see shadows of the emotions of life that she cannot experience due to her seclusion.  (Not only the lovers, but the funeral as well.)  Though her emergence from isolation later results in death, she still triumphs because she is passionate about something.  She took a chance.  Only when vulnerable can a person experience a passion for living.  (My professor said this was a bit moralizing).
• The tower is not a foreboding prison, but a cocoon.  Like the cocoon, the tower lacks outside beauty, but in it the butterfly prepares for emergence into the world.  These images are in the poem:  the Lady "weaves by night and day / A magic web with colors gay."   A caterpillar may stay in a cocoon throughout the entire winter and emerge in the spring, but most butterflies have a brief life span.  (Some only live a week!)  The Lady's emergence from the tower results in a shortened but triumphant life.  And a butterfly she becomes:   "Robed in snowy white / That loosely flew to left and right....  [She floats] down to Camelot."
• When Lancelot enters the scene, the Lady has just reached the point in the poem where she has missed out on a part of life.  She is "half sick of shadows" and here comes Lancelot riding by with all his images of light (the sun "flamed" on his armor, his shield "sparkled," his "gemmy bridle glittered free," etc...).  Lancelot is not exceptionally stunning himself, but all his appearances provide striking contrast to the shadows she has come to despise.   The Lady reacts and leaves because she has fallen in love with the idea of love, not with Lancelot specifically.
• Lancelot is ignorant and shallow in nature.  His anticlimactic commentary on her appearance, "She has a lovely face," seems a shallow end to her tragic story.  In my opinion, Lancelot's character lacks depth.  His only other line is "Tirra lirra"  -- what's up with that?

• The images surrounding the lady are pretty and feminine in nature ("imbowers", space of flowers").  She sings and lives as a "fairy" in the eyes of reapers.  She sits in her tower weaving on a tapestry.  The Lady is the stereotypical Victorian female - private, reserved, mysterious, and let's not forget that she is properly occupying her hands with some sort of craft.
• Masculinity is linked with light.  When Sir Lancelot enters the picture, images of light fill almost every line.  Let's look at light.  For one, they contrast the shadows that exist in the Lady's tower.  Even though direct light makes shadows disappear, true shadows cannot exist without light.  If the poem is saying light is man's real world and shadows are the woman's, then it's saying that women cannot exist in a world separate and apart from the world of men.
• The Lady does not keep the role of proper woman, however.  She takes matters into her own hands enters the 'real' world.  This entrance of the submissive woman into the male-dominated world brings about her downfall (not to mention the destruction of her artwork).  So this is not saying that these roles are necessarily the way they should be.  Besides, as already mentioned above, Lancelot comes across as lacking depth.  The poem reduces it's powerful figure of masculinity to an ignorant, shallow character.  In this turn of stereotype, the poem confuses the limits society sets on gender.
• Gender confinements come across as the cause of the Lady's downfall.   She cannot meet her full potential when isolated, nor can she survive apart from her confinements in the world of man.

This paper was rather different in nature, so I will not hit all the main points, but only a few:

• Even though the poem is set in medieval times, there are references to Tennyson's own time, industry, and commerce.  By the 19th century, the industrial revolution is passed, and technology is used on a daily basis.  The poem, however, reflects not an era of technology, but is full of Arthurian romance (a topic covered heavily in the 13th century).  There are some references however - "heavy barges" were not yet present in feudal days. 
• The connotation surrounding the "barges" and other images of commerce in the play are negative.  The busy inhabitants of this commercial land do not appreciate art.  ("is she known in all the land, The Lady of Shalott."   The reapers, however, an example of the working class, are closer to nature and do appreciate her, and listen to her "By the moon."  The moon serves as a romantic image.
• The "burgher" (member of the bourgeoisie which came with the rise of the middle class) did not exist during feudal days, yet we see him in the poem.   The "burgher" and the "market girls" indicate the commerce and middle class that did not exist yet.  Their world leaves no room for art, and it is of no coincidence that the lady dies when she emerges into this environment.  Perhaps Tennyson was concerned that art could not survive under conditions of commerce and technology.
• The poem is full of both romantic and realistic imagery, but it is the romantic imagery that prevails.  The poem communicates a feeling of nostalgia for the past, and perhaps a fear that art cannot continue to exist the conditions of the technological society of the 19th century.