The ending of Harry Potter and the Goblet of Fire resolves the tournament mystery and then takes the victory away, because the cup Harry wins is a trap. Harry and Cedric agree to take it together as joint winners, and that small act of fairness is what delivers both of them to the graveyard, since the cup is a Portkey. Wormtail kills Cedric, and the film does not soften it: Harry returns holding a body, not a trophy.
The scheme behind it has layers. Barty Crouch Junior, posing as Mad-Eye Moody through Polyjuice Potion, put Harry's name in the Goblet. That is why Moody's quiet advice before the dragon task makes sense on a second viewing, and, in my opinion, it is the best reason to rewatch the first half. Wormtail then uses Harry's blood to bring Voldemort back to a body. It could be argued that this makes the tournament a long route to the graveyard rather than a distraction from the real plot.
The true ending, in my reading, is the memorial that follows. Dumbledore honors Cedric and tells everyone that Voldemort killed him, while the Ministry of Magic denies it. The foreign students depart, and Harry, Ron and Hermione look ahead, aware that dark times are coming. That Ministry denial is the thread that Harry Potter and the Order of the Phoenix picks up directly, when the Ministry sends Dolores Umbridge to teach Defense Against the Dark Arts.
There is also a ratings point. The first three films were rated PG in the US, and Goblet of Fire is the first to carry PG-13, which fits a story that ends with a killing and a resurrection.