Refresh features include: OLED HDR 90 hz Better battery life (50wh vs 40wh) Cooler Lighter Even better performance, even though not advertised by Valve! (because of the better DDR memory 6400mt/s vs 55000mt/s) Bigger screen
Digital Foundry review:
https://www.youtube.com/watch?v=Z1KLj06fn2s&t