The latest issue of Game Developer magazine has a lengthy feature on what went right and what went wrong from the Aion team's point of view. The CryEngine and the game's overall level of polish are both cited as decisive positives for the game, helping the game feel more vital and engaging. The limited amount of flight early in the game is also pointed out as helping to simplify the learning curve, as navigating combat in three-dimensional space can get overwhelming for first-time players.
On the flip side, the developers also talk about the amount of pressure on the frequently-changing team, as well as the technical and conceptual troubles with working on the Abyss. If you're interested in reading the full article, you should pick up a copy of the magazine, which is only around $4 for a digital copy.