Soooo I preordered the game on a whim. You get a PDF of the most recent playtest version (revised), which will be further updated as the game continues to be tweaked. Most of the playtest reviews and impressions I read were glowing, so I figured "what the hell, why not give it a shot?" I haven't gotten all that far into it (haven't even read any of the classes), but I'm sort of wondering whether the preorder was such a good idea.
One can't help but compare it to D&D Next, since the game is described by its designers as "a love letter to D&D," and especially since those designers are Rob Heinsoo (of 4th Edition) and Jonathon Tweet (of 3rd Edition). The game heavily emphasizes story and narrative priority, but it seems like it might have gone a bit too far in that direction. Overall the style of game that can be run seems like it will be a bit niche (at first glance), as opposed to D&D Next's goal of appealing to as broad an audience as possible with modularity. In short, the system seems less flexible than I'd hoped, though I may be wrong on that. The writing does transparently advocate house rules, alternative rules, etc.
Another letdown is that I've become very excited by the prospect of bounded accuracy, which is not in 13th Age. While the escalation die is a good idea, the relatively low-accuracy of PCs seems like a step backwards (to un-errata'd 4E), but perhaps quicker combat rounds will rectify that.
I do like the skill system, which is even more open-ended than D&D Next, but unfortunately defaults to certain classes getting more skills than others (that's getting house-ruled right away!).
The biggest disappointment is that it seems like the Druid might not appear in the core book, ostensibly because of design difficulties. I'd rather the thing be delayed and actually get a core Druid, especially since the PDF will be updated as the game gets more finalized anyways.
More thoughts to come as I continue to read the PDF.