EDIT- This image is post buff. The image reference to the wiki was updated, so this shows the new, buffed Shockwave.
First off, let me say that I don't the card is terrible or that it needs a buff worse than any other card in the game. What I'm mostly basing this on is a comparison with this card:
When compared with lightning, shockwave just seems lackluster. It has the instant kill effect on frozen things, but to get that it gives up both 1 damage and the ability to target players.
Because
has Owl's Eye and Eagle's Eye, Shockwave is mainly gunning to be a splash CC card, but since Lightning is better at that Shockwave sees little use. It's left only as a toss in for rainbow decks that are already running Lightning.
Think about it this way. How many PvP decks do you see that actually make use of the shockwave instakill ability?