I love feats in D&D 3.5. The concept capitalizes on the excitement of exception-based game design such that each player gets to one-up their opponents, or else be one-upped by them. It mirrors a game like Magic: The Gathering, in which one lucky combo attack can win the game. How much do I love feats? Well, I bought UndeFEATable, a book of 500 of them, and it was worth every bit of its $20 price tag.
The UndeFEATable paperback is a collection of previously released Undefeatable titles, each a short list of feats for specific classes or around a certain theme. I don't own any of those, so I don't know whether this collection features extra feats beyond what was published or whether the only selling point is that it's a hard copy.
As I wrote in my Book of Lost Spells review, the obvious tag line to a book of 500 new feats is you can never have too many feats. While I believe that to be true, I know some people find too many choices overwhelming. Between this book, the Pathfinder Core Rulebook, and then extra feats that appear in adventure paths and player guides and other sourcebooks, there must be a few thousand feats to choose from.
Then again, that is, in a way, exactly the value of this collected work of feats: this is a book of a lot of feats all in one place. In a way, you can focus feat selection on this book as a way to prevent overwhelming feat choices for your players. My players often don't own the Core Rulebook, or else they don't reliably bring it to the game. I appreciate Undefeatable for being an easily distributed list of good feats for players to browse when leveling up, while allowing me to either keep my Core Rulebook on hand, or else to distribute the Core Rulebook to other players so feat selection happens in parallel.
Mostly, the feats in this book are very good. Feats by nature tend to apply only under specific circumstances, so a lot of the feats here are only going to get used once in a while, unless a player bases their moves off of a feat benefit. The important thing is, though, that these are quality feats. They're useful, and inventive, and powerful.
Some of them are derived from natural mechanics; the very first one in the book, for instance, is Accidents Happen, which causes one enemy to accidentally attack another of your enemies when you successfully dodge out of the way. It makes sense; if a baddie takes a swing at a fighter, but the fighter ducks, then it's a natural and obvious hazard of battle that someone else nearby might get hit instead.
Others are magical in nature, and so they make no real world sense, but they're exactly what you want. For example, Draining Strike uses necrotic magic to grant your character with temporary hit points while draining hit points from an enemy.
For the most part, I love the Undefeatable feats, although there are a few so obviously limited in scope and benefit that they seem only to serve as obvious choices to not make. Every book of feats have a few of these, and I'm never sure whether these feats exist because the authors literally want a contrast between really good feats and really obviously silly ones, or whether it's a product of too much editing and not enough proofing. The Against all odds feat sounds powerful, for example, but its only "benefit" is that you can reroll a saving throw, but you must take the new value even if it's worse than your initial roll, and you also take damage whenever the feat is used. It sounds more like a curse with an edge of benevolence than a daring feat.
The thing about feats is that if it's not the exact right feat, it just doesn't feel integrated into the character. You might think that a Fist of the dragon feat, which allows a player to roll twice on an unarmed attack, taking the better roll, would be perfect for any character. After all, everyone wants a benefit on an attack. And yet for some player, this just doesn't fit. Maybe a fighter is empowered by her sword, and is less comfortable with hand-to-hand combat. Maybe the chance of an attack going wrong feels suitable for a fatalistic monk. Or maybe it just doesn't feel right to a player. The more feats players have to choose from, the greater the chance of finding the one feat that fits perfectly, in every way, into a character backstory, personality, or role.
A book of 500 Undefeatable feats is a great place to start, so check it out.