I was majorly into this anime when it first came out. Actually, it's what inspired me to start playing MMOs (though I admit that I was slightly disappointed that real MMOs weren't like The World :D). A lot of people were turned off by how little action there was in the whole series, but it made sense if you viewed the series for what it was meant to be.
I can't say that I was disappointed by any part of this series. The whole thing was interesting and entertaining for me. Of course I wished there were more about what the players were like in real life, but there's only so much time in an anime series for information. Besides, that would have been besides the point that the writers were trying to make.
As for Sora,
I can't say I was disappointed at all. A bit surprised, really, but not disappointed. In retrospect it made perfect sense given his reaction towards more mature players (e.g. Krim). I'd suspected that he was young-ish, say in the 15 - 17 year old range since he was much too mischievous and impatient for normal people and his need for attention was pretty obvious. In reality, you could say that he was remarkably mature for his real age. It was cool that his ending in the anime led into an interesting segue in the following games.
The .hack game series was pretty good, too, though a bit too long, I think. they should have knocked it down to two games. They really put a lot of thought and effort into them, though. It was cool seeing how the games affected "real life". .hack//LIMINALITY was interesting, as well. I didn't like how disjointed it was with large gaps and new character introductions being completely overlooked, but it was still a good series.
Everything after that, unfortunately, was a travesty; just another attempt a capitalizing on a fad. That Legend of the Twilight Bracelet crap was just terrible. I've heard mixed things about .hack//G.U. and the anime that went along with it. I had seen some of the anime when it was on Cartoon Network, but honestly I couldn't get into it. I think they should have stopped while they were ahead.
Also, for those that are interested, the novels are all quite good. //A.I. Buster and //Another Birth are all recommended.