Overall, most of the changes to the Z370 chipset is relatively minor. Obviously the support for the new Coffee Lake-S CPUs is a very big deal, but the odd thing is that for whatever reason Intel decided not to change the physical socket from LGA-1151. This means that you can install a Coffee Lake-S CPU into a Z270 motherboard without the need of a hammer and everything will appear to be correct - only the system will never actually be able to POST or operate correctly.
Besides support for Coffee Lake-S CPUs,
the only major changes made are the native support for USB 3.1 and support for PCIe RAID . This may be disappointing for those that were hoping for some cool new technology, but the USB 3.1 support especially is really quite nice to see - especially if Type-C connectors really take off. Even reversible USB connector likely isn't going to be enough by itself to make anyone upgrade from Z270, but honestly the CPUs are what typically drive upgrades, not the motherboard or chipset.