Well, actually, 'Heartstopper' is a graphic novel. It has been widely celebrated for its beautiful illustrations and engaging story that follows the lives of its characters, especially in the context of LGBTQ+ youth experiences. The format of a graphic novel allows for a unique blend of visual and written storytelling that has made 'Heartstopper' so beloved.
It's hard to say exactly what's new without seeing it, but it could be new villains, new powers for the heroes, or a completely revamped setting. Maybe the writing style has changed to make it more engaging or contemporary.