This starts out well enough, despite immediately showing signs of falling into the usual traps--superficially written characters who behave inconsistently, lots of routine jump scares, etc. Still, the photography and scenery are very handsome, and the atmospheric elements are there for a good straight-up slasher at the very least.
But as it goes on, the film unravels, fumbling more and more right up to the fade-out. It raises too many supernatural red herrings that are then abandoned for something real-world yet entirely implausible given the way things have been staged. The scares are utterly cliched: CGI shadows passing in the background or foreground that the characters just miss seeing; repetitive nightmare "visions" in the realm of "Oh my god I am completely covered in blood oops I just blinked and now I'm not;" and other things that, apart from being silly, make NO sense at all when the story finally coughs up its convoluted and ridiculous resolution.
Frankly, a straightforward slasher would have been a lot better than this murky stew of ghost store, incest vibes, creepy-disappeared-brother (who's deaf, which somehow is supposed to be even more "creepy"--a pretty crass notion these days), and standard hot-young-folk-in-rural-isolation-peril stuff. I gather this is based on a much-earlier film and novel that are Norwegian classics, but that this incarnation made a lot of changes to "cater" to modern horror audiences. The result suggests that they either should have gone farther, or stayed faithful to the source material, because what "Lake" ends up being is a mixture of creepy and corny in which all the elements feel underdeveloped and compromised.
Whatever the original story was, it had to be better. Or if it was too old-fashioned to revive, then they should have just made something vigorously formulaic like "Cold Prey." Instead, this winds up never quite deciding what it wants to be, and getting tangled in its own net of not-particularly-complementary ideas until the movie goes under.
