This may not sound like much, but a number of Z170 boards have issues of "if you use X port, it disables Y port". Four more PCI-E lanes should actually go a long way towards curbing this and also opens the door to multiple native M.2 slots. Until recently M.2 has seen relatively light adoption, but the new Samsung 960 EVO and Pro drives are much faster than standard SATA SSDs and are actually fairly cost competitive. We expect to start selling much higher numbers of M.2 drive in the near future so the possibility of multiple M.2 slots on a Z270 motherboard is very attractive.
However, one thing to keep in mind is that the launch of a new chipset also gives motherboard manufacturers like Asus, Gigabyte, EVGA, ASRock, and others the chance to make other improvements to their current product line. So while Z270 by itself isn't terribly exciting, we have already noticed some great improvements on actual Z270 motherboards such as increased adoption of Thunderbolt 3 (which hopefully will help resolve the driver and firmware issues Thunderbolt currently has on PC), reinforced PCI-E slots, and multiple M.2 slots. This still is not anything game changing and unlikely to warrant an upgrade from Z170 to Z270 on its own, but Z270 does still provide some small - but welcome - improvements so there is little reason not to use it if you are in the market for a new system.