Childish. Childlike. That is what Kaguya and Shirogane are. Each other is their own first love. As such, it works so well in this story. It is their first time. They do not know what to do. Naive. High IQ, low EQ types. People might not like what happened in their story. But I like it. It is intentionally dragging so you would want more. Let us put our shoes in theirs. First love is the sweetest of all.
Animation is great. Narration does a great job. OP and ED are perfect as well. Character development is just right. It fits right into the story.