So far, so good. 1:22 of use cost me 17% battery, extrapolated that gives me 8:02 of screen time on one charge. Overnight the battery didn't lose so much as 1%. The S2 I moved away from would've dropped about 60% and 10% respectively.
Pros
The screen is a manageable size for one hand
The faux leather back cover has far more friction in the hand than the plain textured plastic of the S2
The screen is seriously bright and very much usable even in direct sunlight
The interface is very responsive, much smoother than my Note 10.1 2014 Edition
The camera focuses bloody quickly even in low light
The battery is AWESOME
38,500 in Antutu

MicroSD slot - this was critical for me
I've rinsed it off under a running tap - I'm starting off slow before I try it as an underwater camera
It gets much better signal than my S2 and even my ooooold Nokia 6310i from the late 90s - the phone which set the standard for me
The settings menu, which I thought would be a nightmare to use, is actually a brilliant layout. Unused groups can be minimised
The digitizer has been kicked into overdrive and can detect my finger from about an inch away
Cons
The headphone socket is at the top of the phone. I keep my phone upside down in my pocket so from pocket to ear is one motion. I can't do that with headphones connected
The waterproof flap for the USB 3 port can be annoying and feels a bit flimsy
KNOX is a bastard, I cannot root without voiding the warranty. I have a feeling that if I root and need to send it back for any reason I'll have to brick the phone completely
Digital image stabilisation isn't quite as good as optical
The phone rests on the camera, exposing it to scratches. A recessed camera would've been better
All of these cons are as compared to the LG G2 which I actually had set aside for me. 16 GB storage without a MicroSD slot was a deal breaker though, it is far more crucial than all of the cons combined.