The AR viewer was a very pleasant surprise, and makes me super happy I got the collector's edition for Reaper of Souls. It's amazingly well done. I've seen AR stuff before, but there's usually some kind of easily-recognizable graphic like a simple QR code for the device to anchor against. Not so with Blizzard's AR viewer. There's a shield icon that lets you know the page can be scanned, but otherwise you'd never know that there was anything special.
In fact, I only found out about the AR viewer because there's a note about it on the very last page of the art book. It's a shame to think how many people will probably never realize they have this awesome feature available to them.
I don't think this is really feasible for RPGs, unfortunately. Blizzard can do it because they already have all the assets (models, skins, animation, sounds). Making those assets is really freaking expensive, and most RPGs aren't nearly profitable enough for it.
I do see AR becoming very big very soon, though. I imagine that there will be something like Yu-Gi-Oh--a simple game marketed towards young kids--where they can use their phone to watch the battlefield come alive and creatures fight each other.
