Power, Connectivity and Security
The Snapdragon 820 seems to be a generational upgrade compared to the Snapdragon 810 chip (Samsung's Galaxy Note 4 from 2014 has the 810). LTE connectivity will gain a boost with the 820 and Sense ID fingerprint technology will also be a nice addition as the technology utilizes ultrasonic measurements to authenticate a user.
It is a great chip. However, I wonder why Qualcomm selected the series number 820 rather than, 9xx as the higher series would have signaled users from a distance that it is a next-gen chip.