Yeah the beginning was awesome. I loved Classic and SI. ToA is what killed it for me. I played on Gaheris and was a raid leader on the server. Man, oh man. Leading random newbs through those ML runs was nasty.
I loved doing ML7 privately with my guild/alliance though. 9 and 10 were pretty fun too. The other ones were a huge pain in the ass for me, and the worst part was that most of the rewarded skills were PvP-focused. Even on the Co-Op server. Our server TL brought it up time and time again, and they refused to change it for Gaheris.
Before all that stuff, I led server raids on the three epic dungeons in SI. Now that was fun. 100+ people zerging everything. For a while, there was only myself and one other guy who had successfully led raids against all three dungeons.
TG was my favourite, followed by Sidi and then... a long ways away from the other two... Gala.
Edit: I'm such a geek.