Good question Beast. What it brings to the table is another MMO set in a fantasy universe that is on the same playing field as other MMO's in general. It offers some features that are unique enough to be their own, yet stay within the framework of a MMORPG type game that you would feel comfortable playing. It is by no means WoW, nor is it trying to be which is good thing. To many other games have tried and failed to do so in the past.

What makes it unique, you can fly for up to 1minute. That's right you sprout wings and soar on up high to get from point A to point B. It's a nice and fun thing to do to navigate around some things in critical situations. Cool down times are still yet to be set in stone so it could be 5min, 10min or 15min. If your flying way up high and your minute is up, it's pancake time :-)
Aion offers a Human, Elf and Demon races to play. There are four main classes each with two sub classes making a grand total of eight different roles you can play.
Warrior (Templar) (Gladiator)
Priest (Chanter) (Cleric)
Mage (Spiritmaster) (Sorcerer)
Scout (Ranger) (Assassin)

You can check out more on the self-wiki if it tickles your fancy
http://powerwiki.na.aiononline.com/aion