Anna is a point-and-click horror/puzzle game. Your character is a professor of archeology who one day finds a lot of photos of himself with a wife and children, at a cabin in the forest. He doesn't remember any of that, and sets out to find the cabin, which is now haunting his dreams. The game starts with you outside, trying to find the way in.
Like I said, it's a puzzle game. You have to wander around and examine things, and then try finding items that will help you get around whatever obstacle you're facing. In practice, this results in a lot of walking up to something you can interact with, and seeing which thing in your inventory you can actually use on it. The game is a little sparse on clues, even if you set it to give you hints on how to solve puzzles. On the other hand, there are plenty of clues as to what happened there. Books scattered around, talking about folklore or rituals for summoning the Goddess. Paintings that appear, wooden mannequins, masks that alter your perceptions. Shadows that watch you, and sometimes, if you make the wrong move, they do something else. There's at least two forces at work in the house, one that wants you to leave, and one that wants you to stay.
I think the scary part comes from being completely defenseless. If something in this house decides to get you, there isn't doodley-squat you can do about it. There's no button command to protect yourself. On a couple of occasions you can avoid a bad time if you just don't approach the obviously dangerous looking thing. At one point I entered a hall. There was a door in front of me, and to the right, a hallway split by a thin wall. One side of it led to a large room with a fireplace. The other dead-ended almost immediately, but at the end was a vibrating shadow, with noticeable bright spots where its eyes were. I figured what the hell and approached it, and the next thing I know, I'm frozen in place. I can still turn, and when I look behind me, there's several more, I turn again and the first one has moved much closer. Things didn't get any more cheerful after that.
But I guess that's what works. I don't really know what's going on, and neither does the character, so there's at least a sense that I could get surprised at any time. Even when I was playing through sections I'd done multiple times before (because for awhile I was getting every ending except the ones where I actually got to the end), I was nervous. Because I could step into the wrong place at the wrong time and trigger something I hadn't seen before.
One weird aspect of the game is that if you examine certain things, you gain these "intuitions". Which you can combine with other intuitions to help piece more of the story together. You don't have to, but if you don't figure enough of it out, you can't certain endings. So the game lets you decide what's driving you more: your interest in learning what's going on, or getting through it before something scares the crap out of you. The game even, at certain times, gives you the option to leave the house, though that ends the game.
The controls are kind of crap. This is one of those games where you have to get the cursor over whatever it is you want to look at or use. Except the controls are herky-jerky, so it's a real struggle to manage that. I try to gently nudge the joystick and nothing happens, so then I press a little harder and the thing swings too much. Small adjustments are exceedingly difficult. In a game where you don't necessarily want to be in one place too long, being stuck because I can't get the game to recognize I want to interact with the leaf attached to the painting, not the painting itself, is maddening. I tried turning down input sensitivity, which might explain why small movements are hard to manage, but the default setting makes the character swing around wildly, like some kid hopped up on sugar, who is also hooked up to a car battery.
So the atmosphere of the game is good, the music is pleasantly creepy (although they overdid it on the persistent strange noises, they get annoying rather than unnerving), it looks all right, it is scary, and the story is fairly interesting. It's just the game doesn't make itself easy to play, even if you know how to solve the puzzles, and if you have a good idea what you're doing, you can finish in about 40 minutes.