Unified casting progression - multiclassed spellcaster are now very viable.
I bought the print edition and I really liked this part (it was my most favorite part of the game, to be honest). I thought it really solved a lot of the issues with multi-class casters that were patched over by spells and feats in other 3.5 editions. While I am a huge pathfinder fan, Trailblazer is worth a look just for the good ideas about game design presented within.