The new system has a total of 25 ranks, each represented by a Hearthstone minion, the lowest being Angry Chicken. As you win matches, you'll progress through the ranks -- and unlike in the current version of the game, it will be possible to lose rank if you lose too many matches. If you win many games in a row, you will rank up faster than you normally would. At the highest rank, known as Legend, you'll be able to see what your rank within that rank is in comparison to others at that level. While you might be at the highest rank the game provides, you can still compete to become the best of the best.
There are additional rewards coming sometime after the release of the new ranked system. Earlier today we mentioned the card skins, cosmetic customization options for your deck. Further, the developers are also adding "gold" version of heroes -- after 500 wins in ranked play with a hero, you'll unlock an animated version of that hero, adding prestige to your deck of choice.