Although the main camera of the S8+ remains the same as is predecessor, Samsung has revamped the front camera. The S8+'s front-facing cameras features a 8-megapixel camera with contrast autofocus system and a f/1.7 aperture lens. The S9 front-facing camera uses what Samsung calls "Smart AF", which uses facial recognition to make AF more accurate when shooting selfies. Just for comparison, the Galaxy S7 and S7 edge featured a 5-megapixel and lacked that advanced AF system.
An F1.7 aperture for the front-facing camera means that you don't need to worry about getting dark images when shooting selfies in at night or in dark places. The F1.7 allows more light to pass through the lens and helps produce images with better exposure and with lower noise. The reasons that you will encounter less image noise is because the camera will have less need to shoot at high ISO sensitivities.
There isn't any true innovation here, no dual-lens camera, no DSLR-like bokeh effect, just a good camera that can capture very high-quality selfies. I like this offering, although I was expecting more from an industry's leader flagship smartphone. The same goes to the rear camera. I think that most people will love the front camera and I'm sure that the image quality won't disappoint. That being said, I need to show my frustration. Samsung's flagship smartphones already seeing strong competition from mid-range devices that showcase very nice features, at least as far as the camera goes. It's like as long as the iPhone doesn't come with any innovative feature for the front camera, Samsung won't innovate there, because it's not threaten by the other companies. Some companies already have invested more in the front-camera technologies because they are aware that for many people the front camera is more important than the rear camera.
Anyways, bottom line, very good camera specs, but I am waiting to see some sample images of the S8+ front camera to finalize my opinion about it.