Navigation Gestures need improvement and tweaking. They seem buggy and unfinished/half baked right now.
Opening the recent apps through navigation gestures is a "Hit or Miss". It should be as smooth as on an iphone.
Also side/edge swiping for back action also seems buggy and not so polished. We it should be tweaked a bit, so that it gives a polished and richer usage experience.
Cues can be taken from the iphone for this one as well.
Improvement in navigation gestures is very important as it is the future of smartphone navigation and Samsung seems to be struggling to give a delightful experience to the users in that particular aspect.