Stealth: Was good before Vanilla KO and KE because you could just appear out of nowhere and kill a shitty equipped mage. Nowadays, nobody is afraid of stealthed sins, to be honest.. and it's so easy to counter with Cat's/Lupine/Abyss Eye
Cure: Nice thing to do, but remember one thing: debuffs can be refreshed very fast, cure is limited.
Light feet: Good skill, but it's not OP at all especially at duels.. ('cept your run away -.-)
Warriors: High AC, High AP, High HP -> Killing machines, debuffs can fuck them up, but nowadays nobody PKs without a priest, and there are so uber equipped warriors that even duffs don't stop them
Mages: Obviously their Blade skill is very strong. They can deal dmg seriously with it + the stun rate for lightning mages gets OOC after a lvl.
Priests: Nice class to play. BPs with good items are godlike, though it doesn't take shitloads of skills to kill everyone after they have been spammed with duffs.
Rogues: Used to be a nice nuker, but with the items getting better and better, they can't just do normal damage.
After an amount of HP, AC, AP this game is not balanced enough anymore.
Warriors get so much ap, hp, and ac that's unbelievable.
Battlepriests become tank priests with insane debuffs and damage dealing.
Mages become tanks again, with shitloads of stun.
Rogues ac improves, but so does every other classes and rogues are not good enough for what they supposed to be. Rogues should have the highest dmg, with mid HP and AC, so they could deal loads of dmg in little time then have a downtime (BB, Spike, CP on cooldown). Their AP needs to scale a lot better.