Arcane Power is a sourcebook for 4th edition Dungeons & Dragons that offers more powers, feats, paragon paths, and other options for the arcane classes: bards, sorcerers, swordmages, warlocks, and wizards. It is not a stand-alone book; it builds on what's presented in the Player's Handbook and Player's Handbook 2.
Arcane Power is 180 pages, and the production values seem pretty good. The font, layout, and general format is very close to that of the core rulebooks, keeping things consistent.
The content is laid out in an orderly and logical fashion: there's one chapter dedicated to each of the five classes, plus a sixth chapter that deals with feats, epic destinies, rituals, and familiars suited to all arcane characters.
Each of the class chapters contains one to two new build options. The new sorcerer builds, for example, are the Storm Mage and the Cosmic Mage, which draw on the power of tempests and of the cosmic cycles of the sun, moon, and stars, respectively. Each chapter contains a pretty broad assortment of new powers, usually between 4 and 6 of each level.
Each also contains a handful new paragon paths suited to its class. The quality of these varies, unfortunately. Many of them are somewhat bland and workmanlike (although they're rarely actively bad). A few, like the warlock's Entrancing Mystic, rise above the rest, providing flavorful and inspiring options.
The sixth chapter contains nine epic destinies, which likewise vary in quality. It also contains numerous feats across all character levels, 19 new rituals, and a handful of magical tomes to add to your game. Finally, it contains the fourth-edition rules for familiars, which any arcane character can acquire and later enhance by spending feats. The rules make familiars useful and beneficial without making them overpowered/'required' or overly complicated, which is a pretty hard line to toe.
For the most part, the content lives up to its promises. The design seems pretty solid, and the book does add some much-needed options. There is a little bit of "power creep" present, although the main beneficiaries are the warlock and wizard classes, which are widely seen as relatively weaker, so this might balance out.
The biggest weakness is the lack of any index, combined with a minimal table of contents. There's also the fact that the Swordmage class was presented originally in a Forgotten Realms book, and is not reprinted here; only the new powers are present. It's also not in either of the Player's Handbooks, so that chapter will be mostly useless to those who, like me, do not intend to buy the FR book. (Personally, I find the material for the other classes is sufficient to make up for that, though.)
Overall, I'm pretty happy with this book. The content needs a little vetting, but that's no different from similar books for earlier editions of the game, and it meets my expectations. The quality here remains pretty high. If you don't like the fourth edition, nothing in this book is going to change your mind. If you do, you'll find some interesting toys to play with. In many ways, it's more of the same -- it doesn't change the game, it just expands upon it.