I have been using s5 since jan 2015. its kitkat version was one of the best. but when the upgrade came for lollipop 5.0.1, lags overheating, battery draining became much frequent.
but after the release of marshmallow update it again came back to its original state.
PROS
primary camera quality is one of the best. it just shoots photos more crisply
the kitkat version is flawless.
high end games just run marvellously. but games like fifa 16 lag a lot.
heart rate and pedometer are very accurate.
CONS
fingerprint sensor is not accurate
front camera is not that good in low light.
ram usage is too high. it regularly needs to be cleaned up.