I'm normally the guy to hate on people crying for 'nerfs' in any game, and in every other aspect of this game I feel PVP is fairly well balanced.
However I have two issues:
The Heavy armor skill - Immovable
and Heavy armor stealth.
I'll start with the lesser of the two evils; Stealth
I realize this game was meant to be 'fair' regardless of armor choice allowing all players to play how they want without any overly detrimental effects.
However I do not believe people wearing heavy armor should be able to stealth on par with leather/cloth sometime's even better than them. Disregarding the medium armor and certain racial passives that improve stealth slightly, in no way should someone wearing full plate be as silent as someone wearing skin or cloth, it's metal, it's going to clank against itself or an object on the floor no matter how good you are.
To put it simply I feel there should be at least a SLIGHT decrease in stealth ability when wearing 2 or more pieces of heavy armor. It just doesn't make sense otherwise, even if it's only a few meters, no way, ever, should full plate catch anyone paying any attention off guard.
And Immoveable...
This ability is somewhat of a plague to PVP. I think I realize it's implementation was meant to stop the WoW Endless-CC chaining so that you can't literally be stun-locked to death, however it's having an inverse impact - It's both making any form of CC utterly useless (with the immunity granted) as well as has a very very minor 'cost' to use, especially in a build that doesn't use a lot of stam-based skills, making it a nearly infinite wall against CC of any kind.
That isn't it's only pvp sin.. On top of making CC useless, with little/no cost - it grants a MASSIVE resistance boost making anything you CAN do against them nearly useless as it tickles the enemy for next to nothing, and your hardest hitting abilities hot as strongly as your weakest when not resisted.
Most of you at this point, knowing net-trolls are going to reply with "Get good, and/or get Immovable yourself"
That brings me to it's third sin... Essentially, if you DON'T use Immovable on every character you have for PVP you might as well not PVP in the first place - this takes away from freedom of play as you are practically required to have this skill in PVP if you don't want to get steamrolled by CC while taking full damage (minus your own natural resistances ofc)
I think a fair solution would be either:
A) Remove the resistance buff (For pvp only) so that atleast if you cannot CC them you're able to do more than tickle their sides while they sit inside 'Immovable' infinitely until you're dead.

Instead of complete-and-utter immunity to CC, it will block a "CC type" once per use. EG; Use Immovable, you are now Immune to the next Stun, Immobilize, Disorient, Concussion, Knockback. and Silence/Interrupt Once 'each.' (meaning it will block each of those, and any CC I missed once per individual CC but if you are hit with a stun, then a stun, the second stun will actually stun you though you'll still be immune, once, to all the 'other' cc types until you use Immovable again (which would prevent it being used Infinitely.)
C) Instead of outright blocking CC, it will reduce it's duration by 50%
D) Reduce the effect/duration of Immovable by 50% and double the cost when not wearing atleast 4/5 Heavy Armor (As it doesn't make sense that someone wearing full cloth suddenly becomes a super-tanky beast that shrugs off everything)
This ability is part of why Vampires as well can literally take on an entire squad/platoon by themselves... Pop Immoveable, hit a few people, tank a few hits, pop swarm, full health.