Only issue (I use the term loosely) with magic missile is that it is a level 1 spell as opposed to cantrip and at times I struggle to see the benefit of it for its low damage out (3d4+3) I mean you can bash it out with a 2nd or 3rd level slot but even then you are only throwing more missiles not upping the damage. I'm far from a balance/meta game expert but I always think it would be better suited as a cantrip with a constitution/wisdom save attached to it.
Magic Missiles has always been a level 1 spell though, I think its too powerful to be a cantrip as is but watering it down with a constitution save (a wisdom save wouldn't make sense IMO) means that when used for its main purpose, breaking concentration, the defender is making far to many rolls... you have 1 for the initial saving throw, then you have another for each missile to break concentration. Also it would mean an auto hitting cantrip, which would be crazy. Train up 1000 peasants to learn a level 0 cantrip, all cast it at a dragon at once, insta hit, dead dragon.
I think its at level 11 where Magic Missile is out done by cantrips, when cast at level 1 (damage cantrips get boosted on certain level ups) but only in terms of damage. But also need to remember that Magic Missiles can be directed at X targets, where X is the number of missiles you have, a pretty useful ability.
Again though, back to the point, Magic Missile is used as a concentration breaker, forcing the target to take 3 DC10 Concentration saving throws.