I had the s4, which I sold to best buy when I upgraded to the S5. I think there are a few features that made jumping to the S5 worth it. First, would have to be the brighter screen. On the S4 I had issues with visibility outdoors (i.e. couldnt see the screen in direct sun very well). On the S5--outdoor visibility is much much better. Also the phone is a little snappier and the battery life is improved. I think it's well worth it for the upgraded touchwiz. The UI on the S4 just looks so much more outdated.