While "Sir Gawain and the Green Knight" broadly follows the conventions of the romance genre--a feast is interrupted, a mysterious challenger appears, and a knight sets out upon a quest--there are deviations from these conventions. For, conventional romance would have the threat of the challenger resolved and a return be made to the feasting. Instead, the Green Knight puts back his axed head and instructs Sir Gawain to come in a year.
There is also a deviation from the conventions with the ambiguity that runs through the poem, creating a sense of unease in the audience. For instance, Gawain sets out on his quest in the winter and arrives at a strange castle that is realistically described, yet it has ghosts of a white hue. Further ambiguity is created as the castle is described as a sort of Eden, which was the scene of both good and evil. When Gawain is presented to the host of this castle, Hautedesert, the host seems much like the Green Knight.
More ambiguity occurs after the meal when Gawain meets two women, one ugly (Morgan le Fay) and one beautiful, suggestive of a false Guinevere. She is not the chaste maiden, however, and tries to seduce Gawain, who is the ethical one. Later in his meeting with the Green Knight, Gawain learns that the knight is the same as the host of Hautedesert and the false Guinevere is his wife. The Green Knight, who earlier acts as a romance villain with supernatural powers, now is heroic in rewarding Gawain--more ambiguity.
The exploration of Gawain's individuality also is unconventional as he takes the ethical obligation of his code more seriously than such other Arthurian characters as Sir Galahad.
The Romantic era was defined by an idealistic view of mankind, a flair for descriptive writing, a tinge of the supernatural, and portrayal of heroic characters and villians. In all of these senses, "Sir Gawain and the Green Knight" is a romance. Gawain is an ideal hero-brave, loyal, noble, and good to his word. We see him at his best through most of the story. He deals with the supernatural Green Knight, along with other mysterious and foreboding trials on his journey. The writing, as recorded, is full of detailed descriptions of setting, costume, and characters.
Courtly love was the "romance" between a lady, who was usually unattainable in some way (married or betrothed) and a knight. This knight was supposed to love and adore her, bring her tokens of his affection, but never betray her honor or act in an ungentlemanly manner. Kind-of a raw deal for the man, if you ask me. In return, the lady accepted his fawning devotions, and usually gave him some good-luck token for him to carry with him in battle. The knight, armed with his token of affection, fought in her name. So, take all of this and apply it to the lady of the castle. She is married. She toys with Gawain. He finds her attractive, but never oversteps the boundaries of morality (but he does lie about the sash). Then he's off to fight the knight, sash stowed safely away, as a good luck token.