3.) Balance
Thirdly, the server would need to have balance. Now, people normally think balance is just with "classes". In all reality, balance is with every single thing in the game. There is supposed to be a 'ying' and 'yang' to games. Most games screw this up, especially private servers. There needs to be a certain tongue when leveling, an 'eloquence' when leveling. Leveling can not just be moving a piece of paper to point a to b, and then attempting to push a boulder up a 60 degree angle up to point C. There needs to be a sort of exponential growth influenced by a rounding to certain y=mx graphs depending on the displacement from point A. Some servers with rebirth act like a parabola, going fast down hill, but then trying to climb up the hill to level. This is part one of balancing! Pick a level, pick a time frame, pick an exponential growth, and pick limiters. "What do you mean?" In a FlyFF private server, it takes one hour to get to the third job, which all together is equal to 190 levels. However, starting then, to get the extra 45 levels, it takes hours upon hours. You were getting "20%" per kill, but now you get "2%" per kill. This transition happens over ten levels. If you look at other games, you'll notice their transitioning to slower leveling is much different. In fact, a lot of games nowadays rely on a questing system to do the majority of leveling. However, it all has a balance to how fast you level at lower ranges, to higher ranges, doing dungeons to not doing dungeons.
Next thing on balancing is drop lists and the currency in game. This is another thing that is mainly overlooked by 99.99% of the servers out there. People want a lot of drops, which screws up whatever the currency is. "Everything that is worked out in peoples minds are graphs, and mathematical equations, just simply thought on the spot without realizing it", my old sensei used to exclaim. Whenever someone thinks of a large quantity, they think more about larger percentiles and quantities. Have you ever joined a server where hunting items takes ten seconds, but it sells for 500% of the time farming? A server where items are easily obtainable; however, prices are x5 on top of the rate? This is what tends to happen when larger quantities enter. I've probably have lost you by now or you're thinking "that doesn't happen". If you played with me at one point in time, there was a server where I farmed for 30minutes and gave away all the gear and said "they aren't worth selling". "Once you farm the lowest, you're set". Servers overlook the fact that people do not care about supply versus demand anymore, meaning they are getting more greedy. This is why it needs to be balanced. Currency needs worth. Drops need worth, and there is need of a currency sink, to sustain and prevent the over fluctuation of money. Technically, all these "multipliers on rates" could stay at 1x, if you change and alter other things.
Lastly, is the overall balance of gear, classes and skills. Servers that say "balanced" aren't really balanced. PvP is a literal blur. By that, one hit kills and no chance of survival. There are no DoTs. No skill required. Asal one hit kills. People spam infinite healing items to make it last longer. Adoch is overpowered. There's no elemental bonuses to PvP: And people call this balance? Last time I recall, balance in PvP / Gear / Class means each class has their strong side and weak side, and how you utilize them is how you win. If you play other games, you'll notice ways to escape and add distance. You'll notice how something as simple as poisoning and other DoT's can kill a tank. You'll notice that a healer has a chance to kill and live without any 400k pvp damage shield. You'll also notice that each class has a roll in PvE, and dungeons. In servers, blade and maybe healers -> All you need. In retail -> Full stam RM to prevent the boss mobs from switching. Also, no one in retail can tank hits from bosses. These substantial differences should be altered and balanced. A roll of all classes should be applied. Or else, it will be the same fashion fest, money hungry game like it is.