Unbroken
Since other have already pointed out the answer to the orginal question regarding the plethora of movement, I'll ignore that part!
As for the brokenness, nah. In play, my players may charge one time to start that battle, and that's usually it. Occassionally they'll charge the controller or artillery hiding out away from the action, but not usually.
The benefits have been pointed out: +1 to attack, "double move".
The downsides have only been touched upon. The main thing is that have to use a Basic melee attack. This doesn't suit our Dex based Rogue very well. The other thing that was briefly mentioned was that Charging ends your turn. This doesn't sound like much, but it matters more then you'd think. Also, it's hard to charge past enemies without drawing OAs, but that's the same as most other forms of movement.
So in practice, charging is useful for the initial strike, but after that, it doesn't get used very often. There are a enough items and Feats around that you could design a character who's sole purpose in life is to charge as often as possible, though. And to preemptively answer the other usual question that comes up: An enemy usually has 3 squares that qualifiy as "the closest square" since diagonals don't cont as being further away in 4E.
Later!
Gruns