Low light the S4 does not cope so well, but outdoors the S4 camera is excellent, it produces some brilliant pictures, much better than my IP5.
I have not paid much interest in other phones lately, but is the GS4 still the top phone? How does it compare to the LG G2?
It's a great phone, but it's a bit behind compared to the newest phones. The snapdragon 800 based phones have it beat in performance (Note3, LG G2, Nexus 5, etc), and some of the cameras are better, but other than that there's not much in it really.
I moved from the S4 to the N5 and it's an improvement in most aspects, but not one that will make or break either phone for you.
Have had the S4 for 6 months now and I am feeling itchy for a new phone! Don't know which one 
