What I liked most about AC was the open skills trees - there were no classes, just skills that you put together in the way you wanted. Now there were some limiting factors like the number of points you had to spend on those skills, but your build was yours to customize as you wanted. The world was large and open, which was a new idea and I liked the graphics. Monthly events brought big changes to the world as well, like the destruction of towns you had previously gone to regularly, seasons and weather changes, etc that were new to the genre. Combat was dynamic compared to what became the MMO standard.
What wasn’t great was the grouping interface, in that there really wasn’t one. The magic system was very powerful, with the original design that it would be very difficult to use, as each character had their own special reagents needed to make powerful spells, but the code for that got cracked with an easy to use app, and suddenly everyone was able to perform strong magic that imbalanced the game from how the devs had planned it. And the thing that made me stop, in addition to DAoC, was that the devs didn’t mind if the players used exploits, at least until the exploits got patched, which seemed really crappy to those of us who didn’t use them. People got crazy spells and items through exploits, got to keep them after the exploits were patched, and the rest of us who played the game right got father behind the cheaters.
Overall was a great first online rpg experience for me, even if it was mostly played solo.