I'd heard of Valiant Hearts a while ago but just recently bought it for $7.50 on the Steam Sale and played it through over 2 days in roughly 6 hours.

Wow. This game has an incredible story and a beautiful comic-book art style, set in WWI. The actual gameplay is a fun puzzle type game but the gameplay isn't important - the story is emotional and interesting. It follows four characters, an older French man conscripted into the army, a strong American volunteer, a Belgian nurse, and a young German living in France who is deported on the war's start and ends up fighting for the Germans. There's also a dog, Walt, who helps you out with completing the levels. Their stories are all intertwined and the ending is fantastic. Worth every penny, probably even at full price.

A short example of the beautiful moments this game has - at the end of a level set on Vimy Ridge, one of the characters raises a flag with some other soldiers. In the background, two white columns of smoke rise up from the battlefield, looking just like the modern Vimy Ridge memorial.

This is one of the best singleplayer games I've played. Thumbs up from me.