The m8p is screen is more flat now, size also smaller abit (good for me because small hand), more important is battery size is bigger now, battery size is the main reason why i upgrade although I very happy with my 7pro 1tb.
Everybody got a diff reason to upgrade, for me m7p battery was already sufficient for 1 whole day of usage and at most days carrying over to the next day.
I prefer 1 day 1 charge rather than 1.5 days, to me 1.5 days not here not there, unless Ur work is office desk bound where U can always have constant charging.
As for the screen, either it's curved or flat, the again not here not there slight curve really puts me off.
Anyway that's my opinion, enjoy Ur new phone.