Heise have tested the always on feature and say it matches expectations: briefly lighting up part of an OLED screen really doesn't take much juice.
I passed my first S7 poster today and, in a world where Apple seems eyeing the mid-market, it was very Apple. The S6 Edge gave Samsung a recognisable visual USP for the first time and hopefully they'll make sure they produce enough of the curved screens this year.
I think most people will love the SD card and not worry too much about the battery, loading up with power packs if they think they're going to be without power.
As for a dark theme, well Android N is supposed to come with one of these.