I picked up this product to see what expansions of metamagic it might contain, and I was very pleased to find a well-written, well-designed collection of very flavorful feats.
The premise of this collection immediately hooked me: how can Pathfinder spellcasters display the "last ditch efforts of magical will" so prevalent in fantasy fiction? This product has the answer, with ten feats to allow a spellcaster to power up his spells (typically by raising the DC, but also by increasing the caster level or cleverly reducing a target's ability to resist the spell) at a definite cost, typically in negative levels.
My favorite feat is "Power Surge," an obvious Power Attack equivalent for casters that I'm surprised hasn't been captured before.
The feats alone would be valuable, but each and every feat contains a "GM Advice" section that explains how the feat is useful and how to integrate it into a campaign on either side of the screen. Here is an example that spoke right to me: I saw that the Phantasmal Spell metamagic feat only uses a spell slot 2 levels higher, but the Insinuating Spell feat I'd just read uses a spell slot 3 levels higher. An error or poor design, perhaps? Then I see the GM Advice for the Phantasmal Spell feat, which starts with "A player reading this supplement could easily skim the feats and come to the conclusion that Phantasmal Spell is too cheap (compared to Insinuating Spell or Thanatotic Spell) or that the other feats are too expensive..." and then explains why this isn't so. When a "GM Advice" section anticipates a question and answers it fully and directly, that's valuable advice.
There are a few editorial mistakes and a few rules quibbles (I don't see why any feat requires "Casting attribute 13+, Caster Level 1" when it's not of any particular interest or use to non-casters at all), but they don't detract from the overall quality I was very pleased to find here. Less than 20 cents per feat is a great price for this. Five stars.