Well, this isn't a long post, but whatever. In the comic series Planet Hulk, Hulk goes to Sakaar, punches a bunch of stuff, becomes the king, then gets betrayed, millions are killed, he gets angry and causes World War Hulk, in which he goes after the Illuminati which sent him there. The movie is very similar, with small differences, some medium ones (such as Beta Ray Bill replacing Silver Surfer and No-Name not showing up at all), and one big one.
The Planet Hulk comics had to lead into something else and eventually, Hulk had to return to Earth. Hulk is too popular to have him rule another planet in his own comic, instead of smashing stuff on Earth with the heroes we know and love. And so they had to have something bring him to Earth again, and it is one of the most important parts of the story, because aside from everything else, it shows how much he cared about Sakaar, his wife there Caiera, and that he was still the Hulk.
The movie doesn't lead to anything else. They don't have to bring the Hulk back, so they can take more liberties. Instead of just having Hulk get angry and come back, they changed it so that the happy ending actually stayed a happy ending. It makes sense in that they son't want to have another movie dedicated to World War Hulk, and so that this won't end in a cliffhanger, but on the other hand, showing him as king was important and this glossed over that section, but more so, Hulk was the World Breaker, and not the Sakaarson in the comics. He united everybody, but his actions led to the planet getting damaged severely. Hulk isn't just a monster, but he believes he is and this ending was too happy for me. It was a happy ending, but kind of sappy and, well, Planet Hulk's ending really drove the comic home for me.