I've played Aion since like the second closed beta event, and all through the closed beta, the game ran smooth, and I really enjoyed the game.
Open beta, however, has had its share of trouble, plus its highlighted 1 or 2 things they really need to adjust before launch.
First - if you have any trouble logging in at all, it almost always shuts the game down completely. A signle log on can take a couple minutes, so, if you are having trouble getting logged in, you can spend 15-30 minutes just trying to get ready to play the game as you restart the game over and over again.
Second - The authorization server seems to be having its share of trouble. From the log in screen to the character select screen, at any point the game was losing communication with the server and blowing itself out. The problem seems fairly widespread, but it's not affecting everyone, strangely enough.
Third - for most of the weekend, the lag was as bad as any I can remember from any game. Lag spikes deaths very common. They threw up an emergency patch yesterday which definately cured the lag for me, and seemed to for most people, if the in game chat was any indication.
Fourth - I could only play for, at max, 15 minutes before I'd go link dead completely and the game would shut down. I thought this problem was being caused number 3, but after number 3 was fixed, number 4 stayed. I'm not even sure this one is actually Ncsoft related. My isp or my dsl line itself may be the culrpit here. After the weekend I spent actually trying to play the game though, i really didn't feel like trying to troubleshoot this one yesterday.
So, number 3 has been fixed. I'm sure number 2 will be at some point. Number 4 is a game breaker, but I can't throw this one at Ncsoft just yet.
Number 1 would normally not be a big deal, but it really is nasty when combined with any of the other problems. And, sadly, since its probably "working as intended", I don't think this one will get changed