I think people are overreacting to this change.
First of all, virtually nobody took the original 4E Magic Missile. The main reasons to take it were either someone who did not understand the game system, or someone who took a Human Wizard. Possibly.
So, who cares if they changed a power that virtually nobody took?
Now, it has a reason to be taken, especially in Heroic level. It's an auto-single minion kill. Automatically. It can be used to help whittle down a hard to hit foe. The Defender locks the foe down and the Wizard auto-damages it.
Magic Missile, at least at Heroic level, now has a meaning in life.
Now, combine it with White Lotus Riposte.
With an 18 starting Int, that's 10 automatic points per round against a foe attacking the Wizard. 10 auto-damage is a fairly strong incentive to attack anyone other than the Wizard at low level.
And there will be some long range encounters where the Wizard can auto-ping a foe from 20 squares away at the beginning of the encounter while everyone else who does not have a bow cannot.
Even the normal 6 points of damage at level one against a foe can be very useful to bloody a foe, or take a foe out when it is close to those boundaries.
There are some nice feats that work with this as well. Forceful Defense, Solid Sound, Inescapable Force.
And finally, even at higher levels, this is a power that is worth taking. At mid-Paragon and higher, most PCs should be using their 4 Encounter powers and even a single Daily power most encounters. That's 4 or 5 rounds before the At Wills have to be pulled out. By this point in an encounter, an auto-hit power will sometimes be more useful against foes that are nearly dead than a power that may or may not hit, even if it does almost 1.5 times as much average damage. It will be worth it to have one At Will that hits every time. Even if it does not kill a heavily wounded foe, it allows an ally to kill that foe with a single attack.
Personally, I think this is a smart move on the part of WotC. They finally gave Wizard players a reason to take Magic Missile.