The update bumps the OS version up to Android 6.0.1, and the software version up to T817TUVU2BPF1. Android 6.0.1 is the latest general release of the OS, but it will be superseded this summer when Android 7.0 Nougat becomes available.
Along with the various improvements that Google built into Marshmallow, Samsung has of course sprinkled its own additions, such as its TouchWiz interface. Be aware that you may need to re-install some apps after upgrading to Marshmallow; you can do this via Galaxy Apps or the Google Play Store.
And as ever, with over-the-air rollouts, bear in mind that it may take a while for all eligible devices to receive the update, so don't worry just yet if you don't see Marshmallow immediately available for yours.