The gameplay in Age of Conan is pretty stale by MMO standards. Most MMOs that are still running with major updates have long moved on from the "giant slew of abilities" design philosophy that you could get away with last decade, and have come to embrace a leaner set of abilities, that share more synergy.
For example, the combo system could be revamped so that instead of having a large number of possible combos that all only have one set of attacks to execute, a single attack could have multiple effects depending on where you land the combo strikes.
The mage classes could all be significantly streamlined as well, since they tend to have huge amounts of buffs with relatively small effects, and dozens of auxiliary cooldown abilities. What they lack completely is a system that allows the player to apply some skill. Mages could use a system similar to the System Shock 2 psionics system for example to scale the effects of their attacks. For example you could have a spell that is an instant cast on a tap, a full nuke when the button is held for 2 seconds, and a nuke and stun if the player charges it to within a critical zone past 2 seconds. If the player charges too long however and misses the critical zone the spell backfires and does damage to the caster. Powerful effects like stuns or knockdowns would have an immunity timer on the target, rather than a large cooldown.
Since Age of Conan is supposed to be more action oriented than most MMOs I think it's imperative to take that to heart, and get the gameplay updated. As it currently stands AoCs gameplay is pretty stale compared to most contemporary MMOs because there is simply too much emphasis on cooldown juggling and having tons and tons of overspecialized abilities.
Especially with games like Neverwinter coming out Age of Conan just doesn't look like it really has good action in its fights anymore. Everquest Next might be even more devastating if it uses the Forgelight Engine, which can run a full fledged FPS with physics simulation on an MMO scale.