Straightforward, not overly powerful but with a distinct personality, the at-will power Divine Bolts captures, to me, the essence of the Invoker class. A multi-target attack that takes away the risk of friendly fire inherent to most bursts and blasts, it communicates perfectly the fact that an Invoker, more than any other controller, is a team player. Unfortunately, Divine Bolt's career was prematurely terminated with the release of the Divine Power sourcebook, featuring an unneeded replacement in Hand of Radiance, which has essentially the same effect, but is capable of targeting an additional enemy.
Hand of Radiance is too good. Conventional wisdom tells us that damage spread over multiple targets is vastly inferior to focused fire, and that Controller characters should eschew damage in favor of action-negating and battlefield altering effects. Nevertheless, the numbers achieved by The Hand are high enough to override these concerns: three targets should net you a total damage exceeding that of a Twin Strike (the absolute benchmark for at-will damage calculations) by about 50%. Twin Strike is still the better power (or, for that matter, the best), but they are very respectable amounts.
Making it fairer
I'd like Hand of Radiance to remain strong without obsoleting Divine Bolts as it currently does. The comparison with the recently deceased Scorching Burst is inevitable but, as much as I liked it, the Burst had fallen behind the power curve, whereas Bolts are competitive with most other controller at-wills - except for The Hand.
Though toning down the damage is definitely an option, I am more interested in limiting the ability to reach the maximum number of enemies. Currently, and barring very extreme terrain, an Invoker should be able to target 3 or 4 foes from a safe distance without much effort. The change I propose would make this a little trickier:
Hand of Radiance: On the Range line, replace "Ranged 10" with "Ranged 5".
Short range is not an unknown drawback to the Divine power source and, as any Cleric player will confirm, 5 squares away is an awkward distance for a ranged character to be. An Invoker player would now have to choose between the brute force of The Hand, or the relative safety of Bolts - a comparison that probably favors the former, but not as overwhelmingly as before.