Hex was announced for Shamans at the WWI and there's a little bit of confusion out there about Hex. That's okay -- Hex is a little confusing. As explained by the dev panel, Hex is meant as a kind of "emergency" crowd control -- used in the same situation you'd see a Hunter throw a Feign Death or Scatter Shot. A brief moment of "Oh, crap!" to defend yourself, and hopefully your tank (or arena team) will snag that sucker off you before you're dead.
To sum up the spell, Hex transforms its target into a critter. It's fast, just short of an Instant -- Hex has a .5 second cast time. Here's where things get a little more confusing, and where some of the "what the..?" starts. According to some sources, the specifics of the spell read "while moving the hexed target cannot attack or cast spells." That means your victim can either walk, or they can fight. They can't do both at once, but they can still act. From Tom Chilton's description of the spell, a mob will likely completely freak out and be erratic. I took that to mean, however, that a player might be a frog -- but it'd still be pumping out damage or heals while ribbiting at you.
In this sense, "Hex" isn't really crowd control -- it's a more a kind of debuff. It forces the subject to be either rooted in place, or unable to cast or attack, but it leaves the choice of which up to your victim. A new spell is still good news for the Shaman class, but it isn't quite the good news we have been hoping to hear.