I'd say This War of Mine fits quite neatly in the three categories that Scoop brought up: Visually, it's a bleak game with "pencil-drawn" broody and dark filter, fitting the horrors of war nothing short of perfectly. The people's models, in addition, are realistic, and the game also uses realistic photos as portraits for its characters. You'd think it'd create an unwelcome contrast, but it doesn't, and only reinforces the mood of the game.
Both the narrative and the gameplay help each other to the point where the two categories merge: There are a-plenty of games with anti-war messages, but their message tends to be muddled by being power fantasies, where you play as a generic military uber-badass hero. This War of Mine takes a different path and gives you the control over three civilian survivors of the occupation, each with their quirks, but ultimately mundane and human as the game can portrait them. You'll be sneaking around abandoned places to find things vital to your survival (frequently inhabited by bandits or military), whenever it is some wood planks to keep your filter working, food to not die from the empty stomachs, and medical supplies to stave off sickness and patch the wounds up. The materials required for your survival will get scarcer through the game, and going to the new places will always carry a risk of bandits, military, or simply other desperate survivors that want to take that canned food for themselves to not starve. That's where you'll be forced to commit acts of violence and/or stealing from those who are just as unfortunate as you are (and in some cases, are helpless to stop you), which will leave your survivors demoralized and depressed from the realization of what terrible deed they've committed.
Controls are very simple point-and click; click once to walk/sneak/loot/craft/whatev, click twice to hurry up (and probably alert the bandits in the building with the noise you'll make). They really can't go simpler than that, but they don't need the complexity, anyway.
In any case, This War of Mine was a very welcome break from the constant power fantasies and literally the best anti-war game that has been made so far. I consider it a work of art, very bleak and depressing, but also very meaningful and human. Sure, "war is hell" was never a new message in any form of media, but This War of Mine succeeds on the front of delivering and presenting the message by simply taking a different path from "a game about an uber-badass soldier that also has PTSD or some shit", and being all about the human experiences of living under a blockade of a city. It'll be very interesting to see how anyone can do a better anti-war game than this, if it'll be possible.