My wife has had the S6 since launch. It still runs faster in general than my S5, camera is open and snapping pics with the double tap to the home button almost instantaneously.
It is on the most recent update and the signal bars actually show real signal now.
Only problem is battery life...she'll have to charge it by 10 pm just about every day (she uses her phone around 15 - 20 mins every hour). Screen is the biggest battery drain apparently. However, fast charging makes up for it quite nicely - she can have 10% then put it on the charger for 10 mins and have around 60% charge again.
I suspect fast charging is why Samsung feels comfortable with a sealed battery compartment.