Actually, I can't really say why I like the Githyanki so much. I mean, they're evil, and I never play evil, in fact, paladins and rangers have always been my favourite classes... but I don't know... somethin' about them. Maybe it's the fact that they're a slave race who rose up to decimate the race that enslaved them... and the Illithids are far worse than the Githyanki.
I think the Lich-Queen is the biggest problem the Githyanki have. They escaped slavery of the Illithids only to be enslaved again by a lich and whatever connection she has to the Hells and Tiamat. If they were a truly free people, I think they would develop differently and be more diverse in both alignment and beliefs. It would take a little bit of time, but without the Lich-Queen holding their society in fear and stagnation, they would become a better people in time.