Before the Fileplanet beta, Age of Conan had a PvP weekend, which included leveling up to level 6. From that event I had several reports of some classes being overpowered, for example the Tempest of Set. As I like healers, and an overpowered healer would be something new, that Tempest of Set was the first character I tried. And yes, up to level 6 he felt pretty powerful, killing some mobs with a single lightning bolt. Unfortunately the difficulty level of Age of Conan rises dramatically after the level 6. At level 8 you'll find yourself in a solo instance called the volcano, and that one is rather tough. And my Tempest of Set got stuck there, being unable to pass one group of level 8 guards, or even kill one of them before they killed him.
Next I tried the barbarian, which had more success. The barbarian being a rogue sub-class I then wanted to try a warrior class, and went for conqueror, the melee dps warrior class. AoC has a tank warrior class, but I'm not masochist enough to try that in a game with lots of soloing and PvP. The conqueror also performed well enough, although I was a bit surprised how many skills he shared with the barbarian.
I haven't tried any mage classes yet, but I already heard some complaints from people trying the pet classes: pets in AoC don't tank. If you sic your pets on an enemy, the enemy comes running for you, and isn't even trying to attack your pets. So the pets works similar to a damage-over-time spell, not like the tanking pets in WoW. That makes pet classes a lot less overpowered than in other games.
In general Age of Conan is a lot more difficult than World of Warcraft, that is you die a lot more often, even with the tougher classes. And as another measure of difficulty, you need to press a lot more buttons and button combinations than in WoW. So after a while I got tired of twisting my fingers on the keyboard, and started to use the macro keys of my G15 keyboard. That makes the game a lot easier. Which is good news for me, but bad news for PvP in general. Nobody can press button combinations as fast as a macro can, and people with a programmable keyboard like the G15 will have a huge advantage over other players in PvP.
I can see how a more difficult, and more complex to control, game can be attractive to veteran gamers. But when I think of WoW players like my wife, who is calling me in the rare cases in WoW where one has to jump and run because she can't do it, Age of Conan is definitely too difficult for the very casual players that WoW supports. That might make AoC the "better" game from a gamer point of view, but will further diminish the possible player base.