I'm much more impressed with the feats than I thought I would be. I'm pretty much blown away. Now I'm thinking how the Arcane Battle feats would interact with the Psychic's handbook...
The robust treatment of skills and stunts, and especially the DM's Judgement Factor and the Description modifier, are positively brilliant, and exactly what I'm looking to add to my game.
I wish I knew more about Eberron, since the big discussion over the Iron Born seems to be how they stack up versus Eberron's Warforged race. Looking at the Iron Born on their own, I think that they're pretty solid in terms of mechanics and story. On the Eberron front - I have heard some people complain about the plausability of a nation investing so much money in a mere ECL+0 (or is it +1?) Warforged - that issue does not rear it's head in either the ficitonal creation of, or the game-mechanical creation of an Iron Born. The method, mechanics, cost, and limitations keep Iron Born an interesting, but by no means an overpowering or underwhelming, in-game option.
I'm also very impressed that Mearls built an ingenious way for a DM to control the population of Iron Born in his campaign: by controlling the abundance, cost, and ease of obtaining the Codex Ferranium, the DM has a rules-counscious but entirely in-game and story-plausable way of explaining the population of Iron-Born in his campaign.
All-in-all, I think it's a wonderful product. I had high hopes, and it far exceeds my expectations.