"Anna" is an adventure game designed to analyze what the player does and react around his behavior. It features three ending according to how much the character has gone deep into madness. The more you play, the more you find, but to really discover everything, you'll have to lose yourself. With the game, you'll also get the main character's notepad, giving you more insights on the plot, and the original Soundtrack.
If you are looking for intense atmosphere in a slow-pace adventure game, this is what you should be getting.
Speed varies on your intellect and courage. Those that have experience with old style point and click games combining stuff with eachother, will probably get through this with little effort...
However, that's only for the game mechanics.
The scare mechanics are a completely different cup of tea, from randomisations to complete and utter make overs of your surroundings, something very little games share.
TL;DR
A must have for the freaky adventure game freak.