The acts speak for themselves. It's important to note that one guy that he is never played a low rate servers is not worth to discuss such issues.
So, choices like to do are few as reference the issue of rates. If someone chooses to play for long time, he would prefer a low or mid rate server , unlike him who is not able to allocate enough time to play the game so you will choose something more high rate.
Beyond that, there are many examples. This game does not want a lot of consideration and if someone will be interested, his job will be serious. And the results that he'll see. they will satisfy him or even the players that they are playing the server.
A degree of difficulty as the reference leveling you need to have. Beyond that if the quests are working properly, the server must have some difficulty in them. Depending upon the level of each player. Moreover as reference the drops as they grow the level will certainly be more and more difficult to find to keep the interest of players awake.
Corruption for sure, this world should never exist in an alphabet of a serious server. Also there must be installed some protections like Anti-Bot systems, DDoS, Anti Flood etc..
Also the advertising of the server is very important. Can one server may not be so good in features, but nevertheless is a hype surrounding his name and so on it attracts the players. Certainly we are opening a new circle of discussion that talks about the game, played by solo players or from a number of grouped people. In this case iit should be borne in mind that at the beginning of such a game would be relatively difficult to be able to distinguish so there should be a mitigating factor.
After all, it is understood that if anyone is really interested to open a server, he need to have (first of all) a passion to work so as not to leave any unhappy and later some money capital in order to support the work that he has to do. As for the last it's not necessary to be done only by the owner cause the amount is large.