I finally got a chance to run 13th Age, and after 2 sessions my group's Barbarian is very underwhelmed by the class. After some discussion from the community in both the Google+ group, and the Pelgrane Press Forums, I think that the problem is some combination of player perception, partly a suboptimal build, and partly weaknesses inherent with the class.
Briefly, the Barbarian functions best as a crit-fisher thanks to how Rage works, and getting to frequently double your damage will double the value of a large damage die. Using a shield (like my player is), will probably handicap a Barbarian in the long run. Their base AC is simply going to be low, and rather than letting players scramble to get it as high as possible I'd rather see Barbarians have other defensive capabilities to make up for it. Rogues have low AC as well, but they are great at disengaging to avoid getting hit in the first place, and they get powers that reduce damage (usually when they have momentum). That feels right for the Rogue, who was always a skirmisher. What feels right for the Barbarian? Taking those hits and shrugging them off. In other words, tools that augment their HP. Just look at the Orc Berserker - it's a monster with a similar fighting style, and the one trait they used to distinguish it was a temporary HP (THP) mechanic.
The other issue with the class, in my opinion, is that Rage simply isn't available enough. Rage doesn't increase a Barbarian's performance enough past a multi-attacking Ranger or a damage-centric Fighter or Rogue to justify only getting it one battle per day with just a single recharge roll (and a hard one, at that).
Here are the changes and additions that I'm going to use in my games. After a few sessions I'll report back and possibly make tweaks depending on how it plays out. My goal is the change the mechanics as little as possible while still giving the Barbarian a much-needed boost.
The recharge rule from Escalation Edition v.6 reads as follows: "Recharge 16+: After a battle in which you Rage, roll a d20 and add your Constitution modifier; on a 16+ you can use Barbarian Rage again later in the day."
Change this rule to the following: "Recharge 16+: After each battle when your Rage is expended, roll a d20 and add
your Constitution modifier; on a 16+ you can use Barbarian Rage again
later in the day."
Interestingly, this rules change is consistent with the general rules for rechargeable powers in the glossary; prior to this Barbarian Rage worked differently from the other rechargeable powers in that only one recharge roll was allowed.
Assuming a +3 Con mod at level 1, a Barbarian would need to roll a natural 13+ to recharge Rage. So they'd get it in 1 battle out of 4, and have a 40% chance at getting to use it in a second battle using the original EE6 rule. With this house rule, it would benefit a Barbarian to use Rage for his first battle of the day, and then for each battle thereafter he would have a 40% chance of having Rage available.
New Talent - Berserk Vitality
Whenever you hit with an attack while Raging you gain temporary hit points equal to your level + your Con modifier (your level + 2x Con mod in Champion tier; level + 3x Con mod in Epic).
Adventurer Feat: Add 1d4 to the THP gained (2d4 Champion, 3d4 Epic).
Champion Feat: You also gain THP as soon as you go into your Rage.
Epic Feat: Once per battle when an attack depletes you of THP you can heal using a recovery as a free action.
In D&D Barbarians had high HP. In 3rd edition they were the only class that got a d12 hit die, and in 4th edition they were a striker with the HP of a defender. I was, quite frankly, pretty shocked when I saw that the Barbarian got the same base HP as a Ranger, Bard, and Cleric in 13th Age. The only hint of the class's legacy of sturdiness was that their recovery die is a d10 (with an option to increase it to a d12 via a talent), unlike the other classes with a base HP of 7, which use a d8 recovery die. I don't think this is sufficient to make up for the fact that they're a frontliner with a base AC of 12. Only the Rogue and Bard have comparable base AC, and the Rogue comes chock full of defensive tricks while the Bard is only partially a melee class. Granted the Barbarian does have access to Unstoppable, which is a great self-healing talent, but there's still room to expand the concept.
In D&D 3.5 a Barbarian temporarily increased his Con score when he entered a Rage, which resulted in an increase in HP. He also got damage reduction at mid to high levels. In D&D 4E Barbarians get a class-based AC bonus, and certain builds got THP for killing enemies (while all Barbarians have access to various powers that grant THP). The precedent is certainly there, and there's a lot to be said for the aesthetics of the mechanic. This is a guy who is so tough he can wade into battle without much armor, opening himself up with his wild fighting style, but making light of those attacks made against him. Indeed, it is the very act of damaging an opponent that gives him the vitality to shrug off hits. Again, THP is the one mechanic that lets orc berserkers stand out. Should the PC version of the "berserker warrior" be able to do the same?