I've played about 4 hours of this one so far and it's pretty fun, lots of boobies, swearing, Latex wearing Nazis,crazy French accents, Double Entendres and wanton destruction. The main character lives in a store room hidden at the back of the girls dressing room in a naughty French cabaret and it just gets more risque from there:D, If nothing else it's properly Adult, in it's humour and it's sophistication and in comparison it shows GTAIV for the juvenile silliness that it was.
The protagonist is a stereotypical hard drinking Irish racing driver who finds himself caught up in the invasion of France in 1940 by stereotypical Nazis, but this is not a WW2 game like all the others it's all about getting revenge, the Nazis are just the GTA style "cops".
The Saboteur is a blend of generic open world GTA gaming with Assassins Creed style stealth ,Hogans Heroes and Allo Allo (or possibly Carry On Abroad) humour and some pretty slick presentation and art direction, it's definitely worth a look.