The Mini, Maxx and Ultra all share the EXACT same camera. So the review on the DROID Maxx camera is the same as the ULTRA and MINI.
With that said....I have the Mini, I previously owned the Maxx HD. My new Mini takes nice outdoor shots, indoor shots definitely are better than previous iterations of Motorola. Without flash it will take OK indoor low-light photos but nothing crazy. Overall it is very easy to use, takes pictures super fast, and in everyday situations will take nice pictures. Will it take better pictures then a S4...well features aside, the Mini takes similar if not better photos in certain situations. But If you are looking options in the camera settings then you need to looks else where, Motorola's new camera interface/settings is as simple as it gets.