I have had the s6 for a month or so now. The experience has been incredible. I have just flashed the official 5.1.1 ROM from France through Sammobile. It has been a welcome update.
I have just downloaded from the Theme Store the Material Design theme and have been impressed.
I think that the experience overall has been the best of all the phones I have used as a daily driver. I sometimes miss the G3 for some aspects of the UI and the fast way they updated the G3 to 5.0.
I believe if you are considering buying the S6 do not go for the Edge but the classic s6. Personal preference based on the ability to hold well on your hand when typing.
Performance and camera is the best and the UI is great when themed with a hybrid version of Material Design.
I look forward to Android M to be made available ASAP.