From Dusk Till Dawn (1996)
Dir. Robert Rodriguez
Two criminals on the run take a few hostages and head for Mexico. Seth Gecko (George Clooney) is smooth and calm under pressure. His brother Richie (Quentin Tarantino) is a trigger-happy prick who needs protecting from his own impulses.
It's a movie of two uneven halves. For a while it's an edgy crime flick with some Tarantino-penned dialogue. It doesn't go anywhere particularly interesting, but there's at least the feeling that it might.
The latter part of the film, however, has no such aspirations. Instead, it goes all out to please fans of a very different genre.
I'll say no more, to avoid further spoilers, but the direction it takes will either float your goat or it won't. My goat was thoroughly sunk, but credit to the creators for trying something so outrageously divergent.