S8 comes with a spec upgrade, slight updates in software. If you are looking for the best specification then S8 is the best phone in Android platform. And it is also one of the best looking as well. Just note that in India it will come with Exynos processor and not Snapdragon which is slightly less powerful than SD 835.
The display quality is same as S7 but has higher resolution, always on display and it's features are same as S7. Camera hardware is same, there are some minor upgrades on the software though. Battery is a major upgrade in terms of security (rumors are Samsung will get LG to produces batteries for their phones.) The other common flaw, UI is much better compared to previous ones, it is trimmed even further and has minimalist look. You can try the new UI, Elegance UI which is similar to the new UI in S8. The Edges still lack actual use cases, it is more for looks than function. The edge has been upgraded to be more gradual so it feels better than S7, though the false touch issue still remains. Bixby is a good addition but is redundant, again there is not much features in it to make it significant. Future Bixby updates with more use cases and more integration making it better can be expected. For security, S8 has facial recognition which fails rarely but can also be bypassed. Other one is iris sensor which is great. Finally, the finger print sensor is at par, but the location of the sensor. These were some of my observations with the device.
Overall, it is the best android device, price no bar. Personally, I'm waiting for Pixel 2 or even Galaxy Note 8.
Edit : A device mix up between LG G6 and Galaxy S8.