It is one of the better powers, but your game won't collapse. That said, it's still a reasonable pick even if you allow no more than 3 attacks - but I wouldn't punish a player for picking it without good reason, which I just don't see.
To be fair, I regret showing that combo (the one I linked on my first post here) to my players.
I'm running Keep on the Shadowfell for a group of 3 players (eladrin fighter, warlord and ranger). Afraid it would be too hard for them, I ran Kobold Hall first. So, by the time they reached Irontooth they were already lvl 3.
Irontooth went down in a single turn, the ranger didn't even get a chance to hit him.
They're using the same combo over and over (sometimes just not with Villain's Menace since it's daily), and when an Elite or Solo shows up, combat rarely lasts more than 3 turns.
On the other group, a group of 4 PCs, I also ran Keep on the Shadowfell, and also ran Kobold Hall before. They had a harder time all around, almost faced TPKs on several places, where the 3 eladrin team didn't.
What's worse, both groups communicate with themselves occasionally, and now, the fighter from the 4 PCs group is slowly changing his character to use spears (he already changed Sweeping Blow for Rain of Blows, next level will retrain the Weapon Focus (heavy blade) for spear...and then will be only missing the spear itself...)
I wouldn't say it's a collapse, but something is clearly going wrong.