5 out of 5 rating for 13th Age Core Book
I'm not (yet) 100% on board with all the ideas that combine to create the full 13th Age experience, but there's so much good stuff in there, that I'm willing to give it a try.
In fact it may save our (pretty much) doomed 4e campaign. It keeps just enough aspects of 4e to make me want to play it.
It also introduces quite a few concepts that are revolutionary for something that might otherwise be considered a 'D&D clone'.
(I'm rather late to the show, so I won't repeat specifics that have already been reported in much better detail elsewhere.)
The authors also go to great lengths to provide insights into their design process and stressing that pretty much everything should be considered 'optional'.
Don't care for a rule? Ignore it, make up your own, or pick an alternative that they helpfully decided to include, too!
It's not just a great RPG system, it's also fun to read and inspires you to think about your current favorite RPGs and wonder if it couldn't use a couple of of house-rules to make it more like 13th Age...