More cores in this particular case, as Intel finally figured out that they shouldn't make any CPU (core modeling) bellow 3GHz baseline frequency (i5 7400 , 3GHz - 3,5GHz boost). 4 Core CPU's will become a standard when CannonLake comes out. CoffeeLake will probably be boring.
They keep saying about those 15% gain, and actually we could see it only when SkyLake was out, a real core improvement in manufacturing process. This CabyLake and CoffeLake have almost the same core strenght when you clock all Core CPU's in the same frequency and disable Turboboost, Burst and Hyperthreading.... All improvement we can actually notice is iGPU part and its decoding capabilities. They've added no additional execution units, so there's no noticeable gain in gaming.