I have installed W10M on my ATIV. As many said the default windows camera, is the only one which don't focus. Which ofc is a drawback having a physical camera button. Battery life after some tweaking is similar or equal. The vibration on the capacitive keys doesn't work neither, touching them w/o vibration makes the phones feel slower. Like there is no response to our actions. However the overall windows experience isn't slow. Its slower than WP8.1 but we have to understand that what we bought as flagship three years ago is a nowadays low-end, at least in raw performance. W10 comes with a lot of advantages for ur ATIV S. Among them for me the best one is MS Edge. IE was too old. And I had problems loading certain websites. For example www .vueling.es which now i can open on my ATIV. The menus are better organized, i find easier to access to where i want now than with an OS that i have used for 2 years... If you take into account how does the last S.O works on a 3 years old device. (iPhone 4s on last ios...) and that most of phones do not have the chance to get such an update even after 1 year... I think we are quite lucky.