"The Love Song of J. Alfred Prufrock" is certainly no traditional love song, but that is why the poem is so unique. It is a love song as only its titular speaker could create: neurotic, awkward, and filled with uncertainty. This subversive intent is illustrated in the first three lines of the poem proper:
Let us go then, you and I,
When the evening is spread out against the sky
Like a patient etherized upon a table
A normal love poem would make the night seem beautiful. Prufrock is instead uneasy and so evokes uncomfortable imagery to make his point.
A traditional love song features a lover or would-be lover speaking of or to their beloved. They might describe how lovely the object of their affection is, their romantic longings, their erotic desires, and their hopes for the future. They might compare their love to an endless ocean or some other beautiful metaphor. Think of Robert Burns's love poem "A Red, Red Rose," in which the speaker professes a love so powerful that it will last until the seas go dry and the sun melts the rocks.
Prufrock does none of this. The reader never knows who the beloved is or even what they might be like. Instead, Prufrock gives the reader (and presumably, his beloved) a detailed catalog of his own deficiencies: his balding head, his simple attire, his routine life, his self-loathing, and his neurotic personality. He longs to ask this beloved an "overwhelming question," which might refer to a marriage proposal, a sexual proposition, or even just something as simple as a declaration of love, but he is too terrified of rejection to try. He imagines his beloved taking on an attitude of indifference (adjusting a pillow or shawl) and telling him, "That is not what I meant at all," rejecting him entirely.
Prufrock's hesitation and fear make him a subversion of the usual love poem speaker. He is clearly in erotic thrall of his beloved (observing the fine hair on women's arms and "perfume from a dress") and yearns to be the more assertive romantic hero of fiction. He longs to "force the moment to its crisis" during tea, implying he wants to move to the next stage of his romantic relationship but feels powerless to do so in the face of daily routine and his own insecurity. His comparison of himself to Polonius from Hamlet, as opposed to Hamlet himself, shows how minimally he regards his appeal. He can only imagine himself as a minor character in the grand drama of his own life, doomed to passivity, especially in the realm of love.
Unlike the Burns love poem, "Prufrock" does not end with the speaker claiming his love will last until the end of time. Instead, it ends with the image of Prufrock and his beloved drowning as they hear the voices of mermaids singing. Rather than evoking eternal love, Prufrock ends his love song with the would-be lovers dying in the sea, a conclusion consistent with the pessimistic tone of the poem as a whole.
So while "The Love Song of J. Alfred Prufrock" is not a traditional love song, it certainly is a love song, only spoken from the perspective of an insecure, sexually frustrated man.