I have been using my S4 since about 6 months, without too many problems. Same issues as many have pointed out with automatic screen brightness, battery life and "cheap" casing... but that's all acceptable -- or is it for a phone that cost so much ... anyways.
I have a more serious issue now. since a couple of weeks (and I can't trace it back to any change of apps or change in my own wifi network), my S4 regularly disconnects from the wifi network (and goes onto 3G -- I realized it mostly through the higher 3G utilization)... invoking something like 'Wifi disconnected because internet is connection is slow'...
I found one or two threads in other forums about this, and all measures recommended seems to suggest it must be a WiFi router setting or what not. Now the things is, I'm having the exact same issue when connecting to other WiFi networks during travel (e.g. in hotels, airports etc.). So I suppose it must be a phone issue, rather than a wifi network issue.
Any help or ideas?