Warning! Spoilers for The Amityville Harvest below.
The Amityville Harvest ends on a strange note. The horror movie ends on a twist ending that wasn't really a twist at all. Let's break down why the movie's ending didn't work.
The Amityville Harvest is a new installment in The Amityville Horror movie franchise. However, it makes some major changes to the series. The movie follows Christina, her sister Nancy, and their documentary crew as they travel to a funeral home for their next project. While there, strange things start happening to the team. Crew members start disappearing, everyone begins hearing things, and their host Vincent acts very strangely. As they later find out, this behavior change is because Vincent is a vampire. Christina and Nancy fight for their lives as they attempt to make it out of the house alive.
The final scene of the horror movie ends with a lingering shot of the "Welcome to Amityville" sign, implying that this was supposed to be a shocking twist. But, as it was right in the title, this reveal ended up being a failed surprise. That said, The Amityville Harvest could have pulled off the twist if it focused on the why instead of the what.
With "Amityville" in the movie's title, it wasn't a secret that the movie was going to connect to the Amityville franchise. Throughout the movie, Amityville is never mentioned, and nothing along the lines of the series' signature hauntings or possessions ever takes place. The Amityville Harvest ends with Nancy escaping the house only to be driven back by one of Vincent's associates. Then, the camera slows down to capture the "Welcome to Amityville" sign. As this was the only mention of Amityville in the whole movie, it's safe to assume that this is the twist itself. But the mere fact that the movie takes place in the same town as the rest of the franchise doesn't create enough space to build a solid ending.
The Amityville Harvest would have instead benefited from focusing on how it connected to the Amityville franchise, instead of simply stating that it does. As an example, if The Amityville Harvest followed a similar approach to how 10 Cloverfield Lane connected to the original movie, it could have easily pulled off its intended twist. With 10 Cloverfield Lane, fans knew going in that it'd be part of the Cloverfield series, but they were left guessing as to how the movie would find that common ground. By doing this, 10 Cloverfield Lane kept fans guessing until the very end, and it utilized small connections to its predecessor to build a larger, more satisfying reveal that fell in line with the previous Cloverfield movies.
However, with its vampire storyline - which deviates from the haunted house sub-genre significantly - there was no common ground for The Amityville Harvest to find or build on with the rest of the series. Since the movie decided to state its twist instead of showing it, the ending simply did not work.