Agreed. I've been really impressed by every other preview so far; enough so that Nentir Vale is an auto-buy for me.
But this particular monster has three problems: 1) the Bound by Blood mechanic is misworded (simple enough to correct - the flavor text makes the intent very clear); 2) the brothers aren't different enough from a regular troll to be very interesting; 3) they lack sufficient options for a near-paragon elite challenge. Another couple powers, or more differentiation from a regular troll, would have made all the difference.
Again, with an XP budget of 800 (x2) they are not meant to be near paragon challenges, i guess.
I think they make a great challenge for 1600 xp (about a level 7 encounter). As brutes, they work great as a hard challenge at level 4 or 5 i guess. Or a single Troll could be used against a party of level 2 or 3, only to find the same troll and his brother living again some levels later.
The simple design is a good thing in my opinion.
As I stated before, those trolls are nearly exactly how I design my brutes from standard monsters...
I only share Aegeri´s view, when he says, that they are less threatening than 4 standard monsters, as the single target damage is only that of a standard monster, and the multi target attack deals less damage...
when I create those brutes, the burst attack usually the same damage as the standard monster had at this level and i increase the single target damage by 5 or so...
... but i guess melee 2 on a large monster makes that burst huge, and beeing a brute that has high damage and can compensate for low armor with regeneration could make them more than viable.
(Those kind of elites work very well in my game, btw.)