There weren't radical changes to the game engine and how it ran. There weren't big graphical improvements. They didn't change animations very much. Lip syncing was still painful (but the voicework and writing was amazing). There were a number of things that people expect from a AAA launch that just weren't there. I'm going based off of reviews I've read/watch from sources I trust (smaller reviewers) as well as friends.
I'll fully admit I haven't played it since the final stages of beta. I'm not saying the game is bad by any stretch. I thoroughly enjoyed it and felt it was the most interesting game world of any MMO I've played. It had top notch writing and voicework from what I've played/seen, and the cutscenes are fantastic. But there were some base problems that weren't possible to be fixed in the time between the end of beta and launch. My issues with how I perceived the quality of the game was a big factor in my decision to hold off on buying it at launch.
This is all personal opinion mind you, I'm not claiming any of it is fact. But it's an opinion I've seen shared elsewhere so I'm inclined to believe I'm not the only one with that opinion. That doesn't make the rest of the game any worse though, because it's great and I'm super happy a lot of people are enjoying it. I'll probably pick it up some time down the road once things have settled down and the initial rush of players is gone.