Hi Crash - remember seeing you in the GNex forum. Welcome to S4 Land. Just got one of these to replace my GNex and haven't noticed any significant change in signal strength (showing up as -100 dBm 40 asu), but that Sammy for you. Wife's S3 is about the same. I live in a decent coverage area, so dropped calls were never a big issue for me. On a side note, the GPS is MUCH improved over the Nexus. It locks on fast!
Haven't tried the camera in low light yet, but have heard some negative things about it. I'll give it a go when I'm out and about this weekend and (hopefully if I remember - stupid beer) report back on my experience.