The knocked prone is potent, at least. Prone is a nice condition that wastes a move, and gives CA.
It can be potent. But we have found it not to be in almost every fight so far. So far all it has really done is well nothing, they fall down, there up and charge the party. The range of 10(especially since the wizard is usually not in the front ranks) makes it so the targets need to be in the perfect spot for this to disrupt a round of attacks. Also for combat advantage to pan out initiative has to work out well for you so you can take advantage of it.