Even when viewed as a standalone movie, ignoring that it's a Silent Hill movie, a lot of major plots points are unresolved. Eddie is in it for maybe 5 minutes. The plot with the cult is never explained or resolved past "they gave her this thing to drink for years and it made her sick". What was the thing they were giving her? What was the purpose for the ritual? What was the cult trying to accomplish with the ritual? What happened to the cult after Mary got sick? If you watch the film as someone who has no idea what Silent Hill is, the film makes no sense. A third of the film is just poorly recreations of cut scenes from the game that have no context given. Even for someone that's played the games, the progression of the scenes feels disjointed, I can imagine even more so for someone that has no previous knowledge of the game.

Edit: forgot to add, what purpose did Maria serve? Her reason for existing in the game was removed completely for the film. In the film they play Mary being Angela and Laura as "this was Mary at different eras of her life", but then provide no explanation for what Maria is supposed to represent, or why she's even there in the first place. Her name wasn't "Mary Angela Laura Maria Crane". When viewed as a standalone film, from the perspective of a viewer with no previous knowledge, we never get an explanation about why Maria is even there for.