The characters or the heroes themselves?
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Human Heroes
Paladin -- Balanced, but can be a pain when a skilled player learns how to micro-manage him. Same deal with the Mountain King.
Sorcerer -- Rather weak, I think. The only saving grace it has is the summon, and even that is negated with the Spellbreakers from the expansion. It's ultimate should've been a normal ability, I think.
Fire Mage/Blood Elf whatever -- Weird to use, at least for me. While he's got good stopping/staying power with his ultimate and his main skill, Mana Suck should've gone to a hero who actually used more mana, like the Naga Seawitch.
Undead Heroes
Unbalanced as fuck. Each one has a nuke that can do around 200+ damage when fully upgraded; while, combined, their ultimates allow the race to AoE (TWICE with the expansion), Summon a Meat-shield, and summon TWELVE basically un-hurtable units in an instant.
Night Elf Heroes
Demon Hunter -- Disgusting. Probably one of the most powerful heroes in the game if used right. It can kill enemy casters, AoE around itself while in Melee, and then SUDDENLY TRANSFORM into a chaos-dealing badass with so much HP it'll make you cry.
Warden -- A powerhouse if used right. It can teleport around the battlefield instantaneously and kill enemy spell-casters if they're clumped together, or majorly start to hurt your hero with it's venom dagger thing. It's ultimate; wow, it's a walking Doom-guard with resurrection capabilities.
Female Archer -- Weak, useless. Aside form it's overpowered ultimate, its possibly one of the worst heroes in all of existence.
Druid-centaur person -- Solid support hero. What the human spellcaster should be.
Orc Heroes
Melee -- Good at what they do, though the Tauren Warchief always wins out over the Blademaster because it can solidly do more damage all across the board and REVIVE.
Magic -- Hard to decide, as both of them are exceptional support heroes. It's really a decision between their ultimates; in which case the Shadowhunter wins out because it makes you're units INVULNERABLE as long as it's alive and the ultimate is in effect.