"Camera Quality" is a subjective term and it really depends on what the person is talking about.
The Note 4's camera is hands down one of the best cell phone cameras on the market. Features, picture quality, ease of use are all impressive. But like any camera on a smartphone (yes, even the iPhone camera is not perfect) it has weaknesses.
Unfortunately for the Note 4, the weaknesses in this camera are in an area where many "casual" (read: the people who are more likely to take pictures with their camera than any other device) photographers are most likely to want to use it: low light situations with motion. i.e., kids and animals, indoors, in a "point and shoot" situation.
Shooting a sports event outdoors for your kids? No problem. Burst mode and sports mode are awesome. So are some of the effects you can use later on. Sleeping dogs, cats, or kids? Not an issue. Sunrise, sunset? Amazing capabilties.
But if you're trying to take a picture of your 1 year old's birthday party, expect to be very frustrated with the results. If you are trying to get a shot of your dog running across the carpet, unless you've got a lot of passive sunlight in the room, you are going to have a hard time. Even forcing a flash does not always work.
You can mess with settings and make some adjustments, but they produce results that most users are going to consider unacceptable, especially when an iPhone simply takes the picture and it works. It can eventually capture a good photo with low light motion, but you have to do so much work to get there that most casual users are going to think the camera is broken or defective. Especially if they are transitioning from an iPhone or another member of the family has an iPhone.
I'm not sure what Samsung will need to do to address the problem.