24/7 matches. Twenty-four seven server versus server.
Don't forget DAoC, Karos (dead?), Pandora Saga (dead), 4Story (a.k.a. Gates of Andaron - dead?), and Fantasy Earth Zero (... R.I.P.) and the many other games with realm vs realm. I remember playing Regnum about a year before it got translated... It was good for its time.
Some games do not have a big budget, and are good. But that doesn't make every high-budget MMO a conversely bad game. I think high-budget MMOs tend to be higher-quality in multiple aspects.
Fantasy Earth Zero is worth the hassle.