I've been thinking about this some more. Rather than balancing whole classes, I'm thinking more specifically skill improvements.
Promotion system:
A lot of these high level players have been crying for the abolition or heavy nerfing of the system because they've spent so much time playing and grinding promotions, that, guess what, they are so strong the game is now easy. Seeing as the promotion system is the only real progression in the game (because god knows the loot system isn't reliable for that) that would be a huge mistake. I know I would sell the game if that happened, because without something to strive for, I have no interest in this game. With that in mind, I think at least one reform for the system is in order.
Right now, if you want to get cunning, and thus the all-important crit chance, you are forced to play rogues. Ditto for willpower and mages. Then we have the most useless of the three, constitution, for warriors. I personally prefer warrior gameplay, but because I need cunning and willpower, I'm forced to play as the two other archetypes. My idea goes like this- you promote something, and you get an attribute point. This point can then be distributed into any of the attributes, including the class specific ones like dexterity and strength. This would make it equally rewarding to play as any archetype, so you can pick your favorites rather than the ones you must use to get a specific attribute.
Skills:
Lightning Bolt: A completely useless ability. Single target paralysis and damage depending on how many enemies are around? There are zero situations where lightning bolt is more useful than static cage, yet LB's mana cost and cooldown are higher. What? A big decrease in mana cost and CD might make it more attractive.
Poison Cloud: It's been brought up, but it bears repeating- if your team is killing enemies slow enough for poison cloud to be of any use, you're probably not going to make it anyway.
Flashfire: a good idea in theory, but in practice it's too situational. I would suggest that rather than a panic effect, make it a frenzy effect: maddened by the pain, they turn on their allies until the burning effect ends. This way the necro could have two pets 
Ring of Pain: costs too much stamina. Really, it shouldn't cost stamina at all. A simple duration and cooldown would serve its purpose much, much better.
Blessed blades: BB's downfall is its small aoe. Trying to stay inside that little circle in the midst of a running battle is doomed to failure. As others have said, a larger aoe and/or constant, moving effect like bodyguard would be a big improvement.