in the end, the gimpest class (with the division of pvp, group pvp, and high end instances) is rogue, second hunter. Before I said warriors were gimpy..but I was way wrong, at 60 they are very good and useful in instances alike, and group pvp they're pretty badass.
The only thing that is overpowered right now is frostshock, and the druids root.
I agree that Rogues need a little bit of tweaking, but the problem is...they are balanced yet they are not balanced. They are balanced because they have very high potential damage output in a relatively fast amount of time but several means of countering their attacks and defeating them. Because rogues are so balanced, they need tweaking. Same goes for Warrior. Warrior is so balanced that it is gimpy. Though like you said, at level 60, warriors go from crappy to uber because they get new equipment where the other classes don't get much at all. Melee classes in general are crappy in PvP but that is because there are so many casters. It's like a bunch of enforcers without rage trying to kill a nano technician with GSF. Melee just can't get to their targets and pallys got lots of daze attack.
I also agree that frost shock and druid root are two things worth whining about. I could be satisfied if earth shock was left alone for now but as it stands, Frost shock is pretty much the only tactic of Shaman Pvpers. They spam the spell and unlike my frost bolt (though im frost specced so it does slow longer), the target will be slowed for teh entire duration of the cooldown. I forgot to mention the shaman have a 40%+/- [correct me if I'm wrong here] temp form so not only can they spam slowing spells, but they can also catch up and unless you have a mount (obsolete when you enter combat) you will never be able to get away.
Druid root is a tough thing to argue over. Druids are pretty crappy as it is and a spammable root is always imbalancing in a PvP game like this. However from my understanding, they cannot use the root indoors. Which at the high-end game means they're next to useless. Most druids I've encountered stay in caster form and spam moonfire ... only when I'm running from a group and get chain rooted even with blink, will I gripe about their root.
Shadow priests. Up until I respecced frost, I could not defeat a shadow priest for several reasons. One, I'm not undead with my uberleet WotF button which basically says "DENIED" to any warlock or priest who fears + DoT's you which is usually what happens to me. But since I specced frost, I gained a very valuable tool called Ice block. This freezes me in ice, renders me attackless but makes me immune to all damage, removes all harmful spells on me and it mimics the paladins divine shield with the potential to have instant cooldown and longer duration. I haven't tried icce block when feared...not sure it would work but if it did, then there< i can easily beat a warlock or priest. I could use iceblock two times if i utilize cold snap as well (ends all cooldown on frost spells).
But that is just my toolset.
Back to the shaman thing. I didn't say that your heals were good, I compared them to somewhere between pally and druids in efficiency. Druids heals blow...they are all HoT and this game is not an 'over time' friendly pvp game. Low health and no shadowbreeds and other retarded tools make a 1v1 match very quick.
The reason you say 15-20 sec is insane is because you're so used to spamming it. Most of my frost abilities are 15-20 sec and yeah it sounds like a long time but when you're in game it doesn't seem to long. Cone of Cold, Frost Nova... all high recycle times. Plus, doing this would force Shaman to use Lightning Shock (which I wouldn';t mind not being given a high cooldown).
Finally, you're proposal of a 50% chance of ES to stop spell casting.. I'd settle to 40% and 3 second slow timer. Lag plays a big part in this game.