Actually, the Bugbear and Minotaur ability to wield oversized weapons is probably the strongest racial ability in the game (in terms of direct numerical advantage)... but that said, while the Brutal ability is cool for avoiding crappy rolls, I was pleased to see it doesn't drive the average damage up to too absurd levels. (At least beyond what beyond Large does already)
Greataxe (Damage 1d12) - Min Damage 1, Average Damage 6.5, Max Damage 12
Large Greataxe (Damage 2d6) - Min Damage 2, Average Damage 7, Max Damage 12
Maul (Damage: 2d6) - Min Damage 2, Average Damage 7, Max Damage 12
Large Maul (Damage: 2d8) - Min damage 2, Average Damage 9, Max Damage 16
Executioner's Axe (Damage 1d12, Brutal 2) - Min Damage 3, Average Damage 7.5, Max Damage 12
Large Executioner's Axe (Damage 2d6, Brutal 2) - Min damage 6, Average Damage 9, Max Damage 12
Mordenkrad (Damage 2d6, Brutal 1) - Min Damage 4, Average Damage 8, Max Damage 12
Large Mordenkrad (Damage 2d8, Brutal 1) - Min Damage 4, Average Damage 10, Max Damage 16
Each point of Brutal adds an average 0.5 damage per die, which isn't too extreme. While upping the size of a weapon from 1d12 to 2d6 thus doubles the benefit from brutal, it is compensated by the fact that 1d12 to 2d6 is the lowest damage boost from a medium weapon to a large weapon.
Boosting the min damage is its real trick, and that is pretty nice - never being plagued by 1s again will be a boon for many people.
The other benefit comes into play late in the game, with vorpal weapons - that is where the Large Executioner's Axe really shines. Each time you roll a 6, you get to add another d6 to the pot. With Brutal 2, each die has a 1 in 4 chance of rolling a 6 - this not only provides a solid boost to average damage, but makes it awfully easy for a lucky streak to explode into a pile of dice.
Personally, one of my few complaints about 4E is that I really dislike how they handled weapons, and especially weapon sizes. Given the number of [W] powers out there, Small characters seem especially penalized, while Large characters (for the purposes of weapon-wielding) get a rather overpowered benefit. Personally, I'd rather have seen damage sizes go only from 1d4 to 1d12 - adding in 2d4, 2d6, 2d8, etc, just skews the math when you introduce elements like Brutal, Vorpal, Gauntlets of Destruction, etc.
Still, the differences are only a fewpoints in any direction in the end, so the game still works. I just feel they had an opportunity to really make the system work smoother, and failed to take advantage of it.