Six short lines, one simple idea: someone's smile is wonderful, but it becomes something even better when it's directed at the speaker. The poem sets up a comparison that seems to be heading toward a grand claim about how incredible the smile is, then turns it into something more personal. The smile itself is already the high point, yet the speaker says there is one thing that tops it, and that's being the person it's meant for.
The speaker comes across as smitten, a little shy, and completely sincere. There's no elaborate imagery or clever argument, just a quiet admission of how much it means to be noticed and singled out. The short, broken lines slow the reading down, so the final phrase, "smile at me," lands softly and with a bit of surprise. The mood is warm, tender, and slightly giddy, like the feeling of catching someone's eye and realizing the smile is really for you.