If you like fast fights, you should hate the new MM. The damage is nerfed to the point that it's going to slow down combats against anything except Heroic-tier minions, unless you go out of your way to optimize for it.
It's not just a "change of pace", it's a rather major nerf to the power.
(If they made this version of Magic Missile a Minor action, it would be interesting.)
If they made this a minor action it would be super broken.
Let's actually look at some numbers:
Level 1 Wizard, pre-Errata MM, 18 Int: 2d4+4 damage = ~9 damage. Assuming he hits half the time, that is ~4.5 average damage.
Level 1 Wizard, new MM, 18 Int: 6 damage.
Level 11 Wizard, pre-Errata MM, 20 Int, +3 Implement, random +3 damage bonus from feats/items: 2d4+11 damage = ~16 damage. Assuming 50% hit rate, ~8 damage.
Level 11 Wizard, new MM, 20 Int, +3 Implement: 9 damage.
Thus far, assuming a pretty average character and a 50% chance to hit, they seem rather equal.
Let's check a more optimized character, though, which is where the big difference will be felt.
Level 30 Wizard, pre-Errata MM. 30 Intelligence, +6 Deadly Staff of Ruin, +6 off-hand Implement and Dual Implement Spellcaster, Weapon Focus (Staff): 4d4+34 damage = ~44 damage = ~22 average damage.
Level 30 Wizard, new MM. 30 Intelligence, +6 Staff of Missile Mastery: 26 damage.
So overall, assuming you hit half the time, the power hasn't taken a huge nerf. There are downsides - if you hit more often, then the previous version obviously is better. Much more relevant - you can't crit with the new one. That's pretty big.
On the other hand, absolute guaranteed damage is very nice. Enemies have enough crazy tricks at higher levels that automatic damage can be more than worthwhile. Especially since the wizard probably has a second at-will that
does add all the normal bonuses, and they can use whenever it is more beneficial to do so.
I don't really think they needed to make the change. But it doesn't ruin the power and it doesn't break the math of the game. Overall, I think it's fine.