There's a lot of news today so I'm not going to go into the details but you can check out reviews at places like HotHardware, Legit Reviews, PC Perspective and HardOCP.
Here's a short snippet that illustrates how impressed the latter one was:
The GeForce GTX 1070 Founders Edition takes $650 video card performance and shifts it down to the $379-$449 price range. The GeForce GTX 1070 Founders Edition provides GeForce GTX 980 Ti and Radeon R9 Fury X gaming performance to people who could never afford that kind of performance before. The fact that this video card is only pushing towards 250W of system power while giving us the kind of performance that use to come from video cards demanding 100+ more watts, is impressive. It is able to deliver an enthusiast top-end experience with low-midrange power requirements.