The Player's Handbook 3 is Wizards of the Coast's latest Dungeons and Dragons player supplement. Like the Player's Handbook 2, it introduces the player to new classes, races, feats, items, and character generation rules. While these rules are well-implemented and generally thoughtful in concept, a few oversights decrease the book's overall quality.
The PH3 adds the long-awaited Psionic power source to the player's arsenal, and this new resource is very different from the past 4e power sources. Every role is filled, and the overall game mechanics are changed notably by three of these classes in order to provide a unique play experience. Instead of gaining encounter powers, Ardents, Battleminds, and Psions gain power points, a per-encounter resource that can be used to augment many of their daily powers, replaceable at-will powers, and even item powers. These augments might change the range, damage, or control effects of a given power. While it may take a while to fully understand the balance implications of these revisions, at first glance this mechanic appears fresh and useful.
To complement the new classes, WotC included four races for player use. The Githzerai, Minotaur, Shardmind, and Wilden are all in this source book, and are given PH2 style racial paragon paths. These races fit the new classes well, and as usual grant the player a +2 to two ability scores. The twist is that, in all cases, the player is given a choice between two ability scores to increase. For example, the Shardmind always receives a +2 to Intelligence, but the player can choose between Wisdom and Charisma as a second ability score bonus. This flexibility increases the player's control over the character and provides more possible variety in the race roster.
In terms of feats, items, and skills, it appears that the PH3 has the usual fare, with one notable exception. Skill powers allow players to swap utility powers for new powers that correspond to trained skills. This new option is flavorful and makes your character's skills more useful both in and out of combat. As usual, expect to find interesting new items and feats that work well with the new classes and races.
Perhaps the most far-reaching development in the PH3 is the addition of Hybrid class rules. These rules allow an effective combination of character classes starting from level one, and result in more of a 50/50 split between the 2 classes than the PH1's multiclass rules. Every class is given a hybrid write up (features only, so you still need another source for powers), and the player is given rules for picking two of these write ups and combining them into one class. Many notable class features are lost, but some can be regained through the Hybrid Talent feat and more powers and features can be gained by forgoing a Paragon Path (much like Paragon Multiclassing). Hybrid rules do not stop a player from multiclassing into a third class, and this feature could result in some truly interesting three-class characters. Indeed, these rules will strongly affect every player supplement released in this edition of D&D, as every new class and class feature will need a hybrid version printed to be compatible with this rule.
Finally, I have a few critiques to note. First, as I read, I ran into many powers and class features that are not well-edited. The Battlemind in particular may have real problems if the DM does not allow for some slight rule flexibility to make his features work as the rules clearly intend (if you are curious about a lot of these issues, I encourage you to check out the D&D forums). Second, a major inconsistency really bothered me. The Monk, a psionic striker in this edition, does not follow the power point rules that every other psionic class follows. While the Monk has its own interesting mechanics, it could have easily fallen under the martial source given its nature, and it's very disappointing to me that no striker exists that uses power points. Third, and probably most important, the Runepriest and the Seeker feel like filler classes. While they may be robust and interesting in terms of gameplay, they do not fit the psionic mold of the book, and unlike the PH2, the PH3 only adds six classes. These strange new divine and primal additions simply feel out of place, and I think the PH2's approach of adding four classes from one source and two from two others made it a better read.
The PH3 is a buy for players who enjoy D&D and want psionic options, or even for those who just care about hybrid rules. The new player options are plentiful and are sufficiently different from past material that a simple reflavoring of other power sources will not do psionics or hybrid rules justice. A few implementation problems keep these great ideas from perfection, but I certainly hope WotC continues in this general direction for future supplements.