What’s upgraded compared to the S6:
microSD slot.
3000 mAh > 2550 mAh battery
QuickCharge 3.0 > QC 2.0
Always-on display screen( for time, calendar or specific animation)
I don’t like SD so I won’t comment it. But the Exynos 8890 Octa > Exynos 7420 octa:
there are always the 4 x A53 cores clocked at 1.6ghZ but instead of 4 x A57, there are 4 x M1( custom Samsung cores) clocked at 2.3gHz( if 2 x M1 cores are used, they’re clocked at 2.6 ghZ, if 3-4 are used then 4 x M1 are clocked at 2.3 ghZ)
Mali-T880 MP12 > Mali-T760 MP8
Camera has lowered from 16 MP to 12MP to make pixxels bigger & give fast performance for camera auto-focus & shots.
Water & dust resistant( IP 67)