The update though is deemed as critical and your device will automatically update within 72 hrs of downloading the update, if you don’t do it. It actually looks like a precursor or preparatory update to something critical (GDR2, of course). Greg Sullivan from Microsoft has clarified that it actually tests “critical update” capability.
What GDR2 brings:
We received a tip claiming Settings sorting, Mobile data toggle & Cortana for more markets. This still needs to be confirmed with our sources, so take it with a pinch of salt. However, we can confirm Cortana coming to more European markets and the Alpha Cortana in India, Australia and Canada coming out of Beta.
We have earlier reported that GDR2 may bring support for 2K resolution display and Snapdragon 805 processor. However, now it seems the broader hardware support may or mayn’t arrive with GDR2. Microsoft may have it now planned for Windows Phone 9, which comes to developers preview devices in early 2015.