The Samsung Galaxy S8 comes with a 12MP 1/2.5" Sony IMX260 Exmor RS sensor. This sensor has a 1.4-micron pixels, a f/1.7 lens and comes with dual-pixel PDAF system and an optical image stabilization system. So the same great sensor found in the S7 and S7 edge. For me the not so good news is that I was expecting a new camera. The camera is the most used hardware feature for most users. I think that people are always expecting Samsung to innovate in that area as well. I was quite disappointed to see that with all the bells and whistles, there is nothing new in the rear camera, even the camera app remains relatively unchanged.
I am showing frustration about that, but the Galaxy S8 primary camera is still an excellent camera. It was already widely tested and proven to be a stellar for both daylight and low-light photography. So it's not that you are going to be disappointed or anything. The thing is that many phone manufacturer are moving towards a dual-camera setup instead of a single one. Although it's great having a second camera for an ultra-wide angle shooting or having the option to produce a very shallow depth of field effect, a larger sensor with a larger pixels help produce better looking images. I've seen the images taken with many of those dual-lens cameras, and aside from the beautiful Bokeh, I really wasn't overwhelmy excited about the image quality.
Those phones that come with dual-lens cameras use two sensors, and those sensors are relatively small because there isn't enough space to put two large sensor, or it can elevate the cost if a company decides to use two high-end sensors for both cameras. This is why when you pick up a phone with a dual-lens camera, you actually give up on image quality and low-light performance. Even those cameras that come with a secondary monochrome sensor don't do as well compared to the 1.4-micron sensor and f/1.7 as in the galaxy S8.
So the Galaxy S8 having the same cameras as the Galaxy S7/S7 edge isn't actually a bad thing, but I'm sure some people will be disappointed by that. For those of you who just want to know that the camera is great, you have this approval, not by myself, but from all the reviews that reviewed the S7 camera along time ago.