There are a couple distinct differences between dystopian and utopian novels other than just one being happy and one being scary or tragic.
When you read a utopian novel it takes the worst problems of the world and it fixes them. Sometimes the entire world or a hidden community in the rainforest. The society usually functions on high levels with no war, clean cities and at least one underlying issue. Like all “happy” or “comedy” writing they usually end up in some sort of marriage which represents the mending of society. But most importantly there is no way you could imagine what is happening in the book could happen in real life. In a dystopian novel they take the worst points in society and amplify them to the worst extreme. Like all great tragedies they end in some sort of death. Either a physical or emotional death signifying a fractured society. The worst thing about dystopian novels is that it is easy to believe the world could dissolve to such a horrific state.
Both of these types of novels serve a purpose in their cannon. I personally enjoy the dystopian types because of how real it feels that we could end up in that world. I also find it fun to think about how I would survive in such a situation.