It's good, but I'm not sure if it's too good, with one exceptional combination.
I think the power is made for dwarves. They give up an attack bonus for not having a high strength, and they give up an attack bonus for wielding an axe or hammer. Brash Strike basically gets those bonuses back, and at the cost of giving up CA, gives them a chance to do a bit of extra damage. For any weapon talent dwarf fighter this seems pretty reasonable. Good, but not too good.
For sword and board fighters, it essentially gives them the choice of becoming a great weapon fighter when they feel like it, essentially giving up the shield bonus. If I was building a sword and board fighter, I'd stick with some of the other powers, but it's not a bad choice.
For a Battlerager focusing on defense, it's a rather counterproductive choice. Crushing Surge and Tide of Iron (or Cleave) are probably better options, since you probably want to be wielding a sword anyway.
For a Battlerager focusing on damage, it truely turns them into strikers (which should not happen with an at-will power). They make up some of the loss in attack bonus with the +2 from brash strike, and deal striker-like damage, while suffering from a bit of front line striker fragility (if you've seen a barbarian or two-weapon ranger in action, you know what I'm talking about). At first level a battlerager dwarf with a mordenkrad is dealing around 2d5+13 damage with an at-will power (if he has temp hit points which typically does not seem to be a problem). That's better damage than the barbarian who is supposed to be a striker (though we haven't seen all the options for the barbarian yet). A tweaked out rogue can match that damage but he has to have combat advantage. The only saving grace of such a brutal attack from a defender, is that he will be sitting at an effective AC 14, but that's why he has all those temporary hit points.
Of course, take away the BRV build, and suddenly the problem lessens significantly.