An upgrade from the original, 13th Age has long been the best of all the fantasy d20 based games. I had some minor complaints with the original but nothing game breaking. The fighter and the rogue were the big blind spots in 1e and they are entirely fixed and awesome now. Really a great accomplishment.
Overall this is an excellent D20 system, and although I never played the first edition, I'm told this is a huge upgrade. However, the layout of this book irks me and most of my players. The way information is provided for new players is rather unintuitive and sometimes straight up convoluted. It is difficult to find things on demand, and certain things are split between sections in a way that makes for an annoying amount of flipping back and forth. When you're using an online PDF, this is particularly felt.