The title pretty much sums it up. Imagine Grand Theft Auto: Paris, set in 1942, plus you can climb buildings like in Assassin's Creed. Also you need to remain covert as in Assassin's Creed, and by doing suspicious things you will gradually raise the suspicion of the guards until it's time to run away and hide. It's a pretty genius idea when you think about it. Unfortunately there is a lack of polish to the engine that keeps this game from reaching the heights of a GTA or AC2. Odd clipping errors happen occasionally.
On a side note the voice acting is sort of average... The main characters are Irish, French, British or German, and the accents are horrific. I don't think that takes away from the gameplay at all but it is a fun fact if that sort of thing irritates you.
So if you haven't been exposed to the Grand Theft Auto series then this game is going to be a very new experience. For the rest of us who haven't been living under a rock this game is an absolute rip off of GTA. Seriously the objectives the control mechanics, the weapon systems, the vehicles, all of it. the only difference is that everything is circa WWII. The main character has some funny lines and the plot is original but if you're expecting something similar to Assasins Creed/Batman Arkham Asylum gameplay but with guns, then you are going to be disappointed. This game isnt a complete bag of suck, but if you're lookin to sink your teeth into something new and original then this is not for you.