Old chronicles ( no Interlude people got enough interlude servers that open every single day ), low rates , good staff , no donations ( or at least no game breaking ones, and yes change class donations are game breaking -.- ) and , personal point of view , third party programs allowed like OG L2Walker .
Why bots?
You may be asking why allowing bots in server they don't contribute for the good well of the server. Wrong , in my opinion, i think that is very usefull to have a personal buff station. Why? Very simple answer, people these days don't are patient enough to play a support character every single day. You can say "I can", but deep down you, we all know that people tend to create another character so they get some "action" for their own. I know people enjoy to play bishop, and other supporty classes but they get enough of it sooner or later. And when support players tend to disappear, the server tends to die too, but this is just my opinion.
I know that is not easy but i have played in servers, where you could use walker but just allowing the program to buff you,i don't know how, but they could block some feautures like auto-farm and things like that.
Well this was my opinion.