Awesome supplement. I am a big fan of items that grow in power as the players do, and this system delivers on that fantasy. It is fairly crunchy, and I'll admit my barbarian took me by surprise when he unlocked the power of unlimited flight on his greataxe...but he's a Tier 3 PC and you expect that sort of thing.
Nice little add-on system, easy to use, does the thing you want it to do and somewhat replaces the old 3.5e system where you can build magic items by stacking different qualities and bonuses, which I miss.
[5 of 5 Stars!]