Sometimes the phone become hot specially when the phone is charging and I'm texting and browsing 'usually in a dark room so the brightness is 0%'
And yes my phone brightness decreased to 90% automatically and sometimes 80% due to overheating
Lg g2 was faster than g3 and you can see it when you use it for a long time
Overall. Go for it its awesome device
Samsung Galaxy S4 I9505
Samsung Galaxy Tab 10.1 < my last samsung tab they update their new devices & keep old people wait...