This weekend only, SEGA is having a sale of their games on Steam, including the entire Total War franchise! Shogun 2 is 50% off, while the Total War Mega Pack including all games and DLC released before Shogun 2 has a 66% reduced price. A good chance to fill the holes in your Total War collection, so grab it while it's hot!
Is the 50% off based on the £40 Steam starting price (for UK people)? If so it'll still be more expensive than the boxed version (e.g. http://shop.gameplay.co.uk/pc/shogun-total-war-2/_/RM10104/productpage.html). On the plus side, less moral hazard from the Jersey/Guernsey VAT dodging as I think Steam is meant to actually include it.