Saeviomagy
Adventurer
It seems to me that a Level 1 Ranger with Twin Strike and Quarry is way too loc. Basically, with a longbow, you can max out at 26hp on one person in one attach - usually around 14 - 18hp. Add on top of that the feat which adds an extra 10 to his range... woof!
And a rogue can target reflex, have an attack roll 2 points higher and hit for around the same damage. (dagger, backstabber, +4/+2 primary/secondary stat mods).
The only person really falling behind is the warlock, but if the warlock is smart, he can be whacking out 3d6+10 in a round OR controlling the battlefield to a significant degree (if he applies the secondary effects of the infernal or star at-wills properly).
I don't disagree that twin strike is a problem, but it's not really a problem at the levels and numbers you're talking about. Where it really becomes a problem is when you start stacking on damage modifiers and other bonus damage (like crit dice), and the exact same thing happens with every single multi-attack power. Someone striking 3 times effectively get triple benefit from every single damage boost currently in the game, except ironically striker bonus damage.