I pitched this idea to one of the guys in my weekly gaming group, given the five different wizards in Fourth Edition, and all of them pretty much losing to the hunter (ranger) in terms of effective control — a single power change that could be used to make all the wizards better controllers:

I think the current version of magic missile goes like this (Compendium is down):

Magic Missile [Arcane, Force]
Standard action; Ranged 20
Target: One creature
Effect: The target takes 2 + Intelligence force damage.
Level 11: 3 + Intelligence force damage.
Level 21: 5 + Intelligence force damage.
Special: You can use this power in place of a ranged basic attack. If you’re wielding an implement with which you have proficiency, you can add its enhancement bonus to this power’s damage.

I actually preferred the previous version (printed in the Player’s Handbook), that required an attack roll, if only because that way I could score a critical hit with the power, and then my magic missile would do more damage.

As I’ve discussed before, the wizard is a failure as a controller. They don’t do enough damage, their best control powers are locked away behind encounter- and daily-usage rules, and their so-called “versatility” is a sham because it doesn’t do anything about the aforementioned usage problems – powers are used when you use them!

Wizards can change their power load-out, but their usage remains the same.

Here’s how I would change one power, magic missile, to make the wizard a more effective controller (based on the more recent version of the power):

Magic Missile [Arcane, Force]
Minor action; Ranged 20
Target: One creature
Level 11: One or two creatures
Level 21: One, two, or three creatures
Effect: The target takes 2 + Intelligence force damage.
Level 11: 3 + Intelligence force damage.
Level 21: 5 + Intelligence force damage.
Special: You can use this power only once per round.

It’s difficult to summarize all of the amazing things this relatively simple change to the power fixes. First of all, the wizard can use it every round to deal damage to a creature within 20 squares. It’s still a ranged attack, which means it can still draw Opportunity Attacks. That’s cool though, they can take Staff Expertise and never worry again.

Because this power is now a minor action, it forces the wizard to choose between moving and maintaining any other powers they might have. Choices are good, they force interesting strategic changes. The wizard can easily use this power while dazed.

This version of magic missile recaptures some of the flavor of older versions of the spell, since growing in power as a wizard means more missiles. One missile per tier sounds good to me. Sure, it isn’t five, but a Paragon Path could change that.