I just got this phone yesterday.
I love the camera is good light and HDR mode is fantastic. The camera is also very fast, which I appreciate a lot.
In situations that don't have great lighting, the quality of the photos (in auto mode at least) drops off pretty sharply. Noise in lower light photos is understandable, but it looks to me like Samsung attempts to reduce noise by creating a slightly blurry photo, which is annoying. In my opinion, I'd rather have a sharp photo with some noise.
EDIT: I downloaded the Google Camera app. It lacks the features like Samsung's HDR mode, so I wouldn't use it as my primary camera app, but it looks like low-light photos are a bit clearer with it. I think I might use that app for low light photos and the Samsung app for everything else. With that system, I'm pretty impressed with the camera's abilities.