Based on what Ken Choi said, we can supose that quest will be very important part of Aion. There will be as many as it's posible, so that way only by doing them you can get new level. Is it good? I think so. In every RPG game no matter how interesting the fighting is, after long hours of grinding we get bored. But a good storyline can keep everyone playing. It's good that Aion's developers didn't forget what RPG is about, they let the player enter a world of adventures, as opposed to other games where you're just waling around with a half-naked elf killing hordes of orcs/deamons only to fight a big, evil boss at the end. Quests are to provide you with some objectives between levels. They say that if we look back we won't think about hours of exping, but about interesting story which our character has gone through.
We can split quests into 2 groups: campaing and side-quests. Side quests are to be about everyday life in world of Aion and contain only short part of the whole story, but many of them will be conneted with other side quests, so that the build a story togather. Campaing quests are to offer a really big part of the entire story about war of 3 races and development of our character.
Pre-view shows us that in most of the quest we will have to stand on the one of the sides, but there's no perfect one and every choice will bring some consequences with it.
If devs really aproached storyline as the one of most important elements, we'll get something real good. So let's wait till we get some more details and of course the release of Aion: The Tower of Eternity