Lets look at the 2 hard CCs we have: hex and cap totem. First of all hex breaks on damage, single target, 45 sec cooldown with cast time. Cap totem is 5 second delay from where you are first standing and short range. Needless to say if you compare this to any other classes hard CC these are laughable compared to the tools they have.
We have zero skills to increase our mobility. Our frost root is flawed because if you want to keep someone frozen you can't flame shock (which = no damage for ele). Our earthbind can be easily auto attacked the instant you notice the effect. Grounding totem eats one spell on cooldown while other classes get much more potent forms of spell protection (warriors, dk, rogue, hunter). Not to mention the damage shields spriests and mages have. Wind sheer is pretty good but its nothing special, it is standard on other dps. Thunderstorm is only good for knocking ppl off cliffs because it is so unreliable. If you use it to get a melee off you they will be back on top of you literally 1 second later.
Basically any way you slice it, shaman is sub par. The reason is there are two halves that make a good pvp dps: damage and CC/utlity. Shaman has good damage even if its RNG, when the stars aline you can do some crazy burst damage. But the second part (cc/utility) is the most important because it allows you to control fights and turn them in your favor. Shaman is completely helpless in this regard.
Its nauseating when you look at all the tools mage/lock/spriest have and then compare it to a shaman. You read through their talents and it seems every other one you find yourself thinking 'wow that is powerful'. Then you look at shaman and literally not one talent 'wows' you.
I know QQ L2P etc etc. I enjoy my shaman and still intend to main him. I've just accepted that he is a 2nd rate pvp dps and will only be fun against bad players in random battlegrounds when they ignore you and let you cast on them.