I've had my N4 for over 24 hours and my initial impressions coming from a S3:
The screen looked extremely washed out at first but using it more my eyes adjusted. Going back to my S3 showed how over saturated the AMOLED display was, so much so I had to adjust the settings on my S3. But there is no delaying the N4 needs some gamma adjustment. Compared to the iPad or HOX the colours on the N4 looks flat.
The N4 is is thicker and heavier than the S3. But I don't mind that as it gives a more premium feel. Having glass on both sides is nice but my N4 will be homebound until my screen protector and bumper arrives.
The first thing I did was root and install the PA rom and matrix kernel. After my first full charge I managed over 5 hours screen time, which is on par with the S3.
There's still quite a few features I miss from my custom S3. But as the Rom matures I hope to see some interesting stuff.