Martial Power 2 is the second supplement focussed exclusively on the Martial classes in D&D; the Fighter, the Rogue, the Ranger, and the Warlord. As such, the book is almost all mechanical options and if you aren't interested in that this probably isn't the book for you. On the positive side, the design of 4e has clearly improved as the designers have gained experience with the system and Martial Power 2 is no exception, providing many inspiring options for building a character or providing mechanical support to a character.
The Physical Thing
Martial Power 2 is a 160 page glossy colour hardback, costing $29.95. The book itself is clearly and cleanly laid out, and the art is evocative and kinetic with a reassuring lack of random armour spikes and, other than the front cover, the cheesecake armour is limited. In short the whole thing is good - but not out of line with the quality of other 4e products.
Inside the Book
As is common with the Power books, Martial Power 2 is divided into one section (about 25 pages) per class with the remaining 60 pages being generic. Each class has both new class options and the ability to swap out previously existing options - for the most part these are useful, evocative, and well supported by the powers. The general section contains RP advice, combat styles for PCs with a focus, feats, Martial Practices (i.e. the martial equivalent to rituals), and a few epic destinies. Like most 4e books, it is therefore pretty generic at a macro-level and stands or falls on the details - which range from good to outstanding. I'll go through chapter by chapter outlining what's been added (other than some nice, if basic advice).
Fighters: The new feature for the fighters is the Brawler; a fighter using sword and fist to grapple, punch out, and generally disrupt the foe. A very interesting and inspiring option that really increases the control at the cost of lower damage (one of the At Wills allows you to grab your target and hit them on an opportunity attack). This has all the power support you'd expect including eye gouging, headlocks, charge and wrestle the foe to the floor, and a utility with the ability to grab a foe and pull it in the way of an attack as an interrupt. A very cool option, and even the non-brawler powers emphasise the physicality of the fighter over the damage. All very good without adding noticeable power creep.
Rangers: With Martial Power 2, they have effectively completed correcting a mistake that reaches back to the PHB1. The Ranger has now been separated into two separate classes (one dexterity, one strength), each with two builds that can simply use each others' powers (and both can be beastmasters). The dexterity ranger gets some melee powers, most of which are for distracting the enemy to back out of combat (the at will allowing a shift 2 on a hit as long as you don't end up next to the target) and a class feature allowing them to swap weapons fast - from bow to two handed sword or axe (the Dexterity melee powers all being for single weapons). The strength ranger is, of course, two weapon, replacing prime shot with a bonus to hit for moving and the new fighting style revolving round the savage combination of main weapon and an offhand thrown weapon. You therefore now have two viable classes that don't need to borrow stats, and both the weapon swapping and the throw-and-charge builds are good; a huge improvement (although errata has toned down the Throw and Stab at will). The power creep is therefore minimal, but the increase in flexibility and viability from this book is huge - again perfect for a supplement.
Rogue: In my eyes, the only disappointing class in the book. The new build allows easier hiding, and there's the option to switch dagger weapon talent with crossbows - the two combining to create a sniper who readily gains combat advantage from stealth. I've not seen a crossbow rogue in play, and worry that the talent plus the damage dice for a superior crossbow might be too much for a class expecting the dagger's damage dice. Still, a rogue that can outhide anyone else (with the possible exception of people who bring their own concealment) is a nice addition to the stable.
Warlord: Warlords have probably gained the largest expansion from Martial Power 2; two approaches at opposite ends of the spectrum. There's the canny and insightful warlord who focusses on noticing and avoidance and the more lightly armoured archer. Also there's the battlefront leader, which means you can have a warlord in scale and with a heavy shield without too much trouble, allowing Bravura (and other) warlords to finally not be too squishy when on the front lines. In addition to the useful and thematic powers here, there are now enough powers that it's possible to create a warlord who never rolls an attack roll, instead giving away all his attacks (although that requires Dragon support). Like two of the other three classes, the design space has been massively expanded in ways that were previously barely possible and are almost entirely in keeping with the archetype.
Fighting Styles: The fighting styles are a nice addition - they serve two purposes. The first is to make weapons that would otherwise be edge cases viable, and the second is to subtly provide recommended builds for people lost in all the existing options by providing a benefit (and hence pointing out) a string of encounter powers that go with the weapon in question. Not something I'd use routinely, but something that might be very useful for people who don't enjoy all the choice in 4e. The one downside is that each set of feats augments an at will - and augmenting the fighter's Cleave with a Push 1 for a polearm can have some very nasty consequences at Paragon. But overall they look useful - fluffy and simplifying characters for players that want it while providing options for players that thrive on options.
Feats Some useful ones, but little out of line with previous books. Nothing stands out as obviously broken, although I'm a fan of Disheartening Ambush, which gives every sneak attack the option of being rattling at the cost of one dice.
Martial Practices. This was the only part of the book I found actually disappointing. Most of the practices do very little; in some cases less than you'd expect from normal skills. On the other hand they often provide extra options and the cost is normally just a healing surge (rather than the gold for Rituals) and many of the practices (such as Peerless Exploration, allowing you to thoroughly map a 1 mile radius without risk in 1 hour or Warded (tripwired) Campsite) are pretty useful for a feat and a one off cost of gold.
There's a huge amount of additional flexibility provided for members of all four martial classes in 4e by Martial Power 2. The book is well-written, well balanced, and inspiring. I can't think of more I'd ask of a splatbook. So far in my use of the book I've found a lot that's useful (class features, powers, and feats) and almost nothing that I'd ban. Every single one of the chapters other than the one on Martial Practices has so far proved useful, and I intend to try them out next time I have a martial character with a feat free.