The movie was a very marginal re-telling of Silent Hill 1. The beginning scene, where Rose is in the alley, is a very accurate re-creation of how the game opens.
Then it's all downhill from there. They incorporate a few scenes from the games (and some cameos of characters from Silent Hill 2) every now and then, but it's largely a "whole new story".
The cult is absolutely nothing like they were in the game, in the game they were actually behind the creation of Alessa in an attempt to usher in a new Apocalypse.
The ending is nothing like any of the games' endings at all.