The errata document for D&D 4E has been updated again, with many well-deserved fixes, including material from recent books such as Primal Power, as well as long-standing problems from the first Player's Handbook. Several popular character builds will be affected by this, though, with a few exceptions, all are moving from an overpowered position to a reasonably playable one. You can see a selection of the most relevant points below, but you definitely want to take a look at the whole thing!
Wizard characters are taking a major hit, since both a class build and their strongest at-will are toned down. First, the Orb of Imposition class feature is changed to what it should have been from the beginning - a one-shot penalty to a single save. As originally written, OoI was too easily abusable for locking down enemies during whole encounters, with stunning ongoing effects that they had no chance to save for. This tactic has become almost impossible to achieve, since most of the magic items that were used to penalize saving throws in combination with the Orb have been taken down, as well.
The other great loss for wizards is the spectacularly effective at-will power Winged Horde. Capable of almost everything a controller could wish for, this friendly-fire area damage spell with a great controlling effect overshadowed other choices. With its damage significantly reduced, it still does lots of awesome things, but you'll want a backup power when you need to hit harder. I personally would have preferred to see the obsoleted powers brought up to this new standard, but I guess it was not to be. The good news are that the rumors about Scorching Burst's death were greatly exaggerated.
The change to clerics was understandable. Up until now, a strength-focused cleric was about one thing: Righteous Brand. The attack-boosting melee power was ridiculously good, virtually guaranteeing auto-hits for one of your allies' attacks each turn. It was hard to justify skipping Brand for a turn to use an encounter power, never mind another at-will. Now, to be fair, Divine Power introduced a decent alternative in Recovery Strike, allowing you to shift into healing mode when needed - but Brand was still the default choice, by a mile.
No more. With its bonus brought down from somewhere between +4 and +9 to a very generous +3, the Brand is a very solid option that I can use without feeling dirty. Oh, and the dozen domains that boost it in Divine Power feel less like a cruel joke, now.
Other than that, epic-tier clerics will find out that their one-hit solo-slaying power, Seal of Binding, has lost its enemy-damaging capabilities. Now it is merely a way of temporarily removing both cleric and monster from the battle, if you have some means to gain regeneration.
3- Hide Armor Expertise
A change with severe implications for Barbarians and Druids is the downgrading of the primal feat Hide Armor Expertise, which now only grants a minor defensive bonus for characters with null Dexterity and Intelligence. From a Barbarian's point of view, the feat provides Chain-equivalent defenses at very low levels, but becomes inferior to heavy armor as soon as a character gains access to masterwork armor with +2 enhancenment bonuses, so it is unlikely to see much use beyond that point. The other build that is affected is the Swarm Druid, who has no real alternative if he chooses to ignore Dexterity. These characters will find that their AC is more or less acceptable at heroic tier, but really falls behind at paragon and heroic, bordering the auto-hit territory at level 30.
Of all the changes in this rules update, this one is by far the most controversial. Although most agree that the previous iteration of the feat provided excessive AC in combination with Barbarian Agility, and the way swarm druids outperformed guardian druids was less than ideal, it is hard to give up such great defenses. In my opinion, low-dexterity barbarians will be able to manage just fine and don't really deserve any more help from a single feat, but swarms will have a harder time. Maybe the feat should have increase by one or two points at higher levels.
Finally, it should be noted that this fix doesn't completely remove the problem with a Barbarians' excessive AC. Whirling Barbarians can still go beyond the AC of any shielded defender, and other builds can choose to give up their secondary abilities in order to max dexterity, so some kind of errata on Barbarian Agility is needed.
4- Paragon Paths
The Blood Mage paragon path has seen its Blood Pulse power, infamous for its ability to deal ridiculous damage through forced movement, reduced to sane levels. In what is probably overkill, the power's effect has been limited to voluntary movement and its damage has been reduced to a fixed amount in order to prevent damage roll bonus stacking.
Also, the Student of Caiphon path, which was commonly taken for its ability to grant an expanded critical range to divine characters (and anyone with a Radiant Weapon, for that matter) now only provides this bonus for Warlock powers. One overpowered Path down, but there's almost a dozen left.
5- Epic Destinies
The Demigod epic destiny loses its infinite encounter powers at level 30, merely getting one encounter reload. That ability should have never existed in the first place - I can't agree with the abolition of at-will powers when you reach a certain level. Maybe this will encourage more players to try different destinies, since Demigod is, without a doubt, the most popular in the game.
6- General rule changes
The various Expertise feats are now typed as feat bonuses, so that new ones can be released without the awkward rules text stating that they don't stack. As part of this change, all expertise-like feats that granted +1/+2/+3 bonuses to attack are also typed so that you can't benefit from one of these and one expertise to boost your hit rate to the stratosphere. These previously broken feats will now only be useful for strongly thematic characters, who might use them to gain the benefit of two feats (they also grant a Weapon Focus-like damage bonus) for the price of one. As part of this change, feats that used to grant a feat bonus to attack become untyped - so Hellfire Blood, among others, is now more interesting.
The update also includes clarification on how weapons used as implements (and viceversa) work, as well as damage type-changing effects. These now replace previous types, and explicitly allow the use of energy-dependant feats or powers. The most popular application of this rule, Frost Weapons with Lasting Frost, sees a minor adjustment which doesn't prevent it from being extremely potent. Finally, untyped bonuses from sources with the same name (say, a certain feat or power) no longer stack, which addresses issues with feats like Echoes of Thunder.
Several very exploitable items have been fixed. Salves of Power, which granted extra uses of daily powers, now only affect encounters. Solitaires granted very strong powers on the first crit of each encounter, and are now limited to daily activations. Potions of Clarity, which could provide reliable and inexpensive boosts to any attack, now are restricted to encounter or daily attacks of certain levels. Finally, Diamond Cincture loses the ability to heal without expending healing surges.