The main feature of the new Geforce 347.88 WHQL driver is added support for the new GM200 Maxwell-based Nvidia GTX Titan X, currenetly the fastest, and, at $999, the most expensive single-GPU graphics card on the market. In addition to the added support for the GTX Titan X, the new Geforce 347.88 WHQL driver also brings optimizations as well as a new SLI profile for Battlefield: Hardline.
Not to make it all about the GTX Titan X and Battlefield: Hardline, Nvidia has also added a couple of other new SLI profiles for games like Life is Strange, Medieval Engineers, Trine 3 and Zombie Army Trilogy.
You can find the new Geforce 347.88 WHQL driver over at Nvidia's Geforce.com driver page.