I'd thought the same of my S4 AND S5 compared to my S3. on both newer devices, they've added a TON of settings options and a lot are defaulted on. consequently most seemed to me to result in a lower picture quality.
I make sure to turn OFF the Burst Shot, Picture Stabilization, and Selective Focus options. my satisfaction with this phones camera is much higher than the S3, and picture quality seems about as good as a similar point and shoot.
megapixels isn't everything though unless printing in native size, which most do not. I have a Nikon DSLR that's about 8 years old now, a D40. hands down it takes much better pictures, at 6mp.