Eh, A good online game (When it comes to MMOG's) needs to have this IMO.
1. Absolutely no skills at all, like blade skill, blunt weapon skill, blocking or such. Instead it should work like this: The longer you hold the attack button, the more powerful the strike will be. Striking certain points would generate more damage than striking other damages. Weapons like blades could have a higher chance of critical damage than blunt weapons, but blunt weapons could have a higher base damage instead. Blocking would work so that the longer you hold the block button, the weaker it would become making it important to block at the exact right time. You should also be able to block and attack in atleast 5 different directions.
2. Stamina. When you get a shortage of stamina you would attack and block more inefficiently, and be more vulnerable to attacks. More effects could be placed to make it more or less realistic.
3. Real-time fighting, or strategic simultaneous fighting (like in Toribash). Otherwise the removal of skills doesn't matter. Also, no dice system.
4. A working and to some extent realistic economical system.
Ok, now for what it doesn't need.
1. A good story. A good story helps, I'll admit that, but if the players want a story they can create one for themselves.
2. Good graphics, but it certainly helps.
Now for something that it should never have:
Idiots.
---
If anyone can point me to a game like this I would be eternally grateful.