Some of the qualities a good MMO has are:
- An engaging story
- Quality PvE encounters from level 1 to the cap.
- An achievable end game
- Balanced PvP throughout the game
- A rewards system for those who have done 'everything'
- And probably a lot more.
I'm going to go over, in brief, why each of these is important and in later posts I can more fully flesh them out. So, number one one the list is an engaging story. Now, while many people say that don't care about the story, then why are they playing a game and going out to fight dragons? They care about the story, even if they say the don't. If the only reason they're playing the game (I'm thinking of WoW here) is for getting better stuff, why aren't they out in the real world, getting better stuff in real life? If you don't have a story, you don't have players.
Second, I have Quality PvE Encounters throughout the game. If the game is just killing boars that auto-attack you until you get to the cap and then you have dragons who auto-attack you, its going to be boring. If you have boars auto-attacking to the level cap and then things get interesting, you're going to lose a lot of people to boredom. Adding quest chains like the one in Redridge or The Day Deathwing Came (Both from WoW) help alot. The rift events, and even the rifts themselves (From Rift) keep the game from being a grind-fest. Now, these have their problems, but I can address them later. To match Quality PvE encounters is Balanced PvP. Player combat is almost required, as it is as close to a direct competition you can get. In PvE and world/server first races you have competition, but it is not direct. If PvP is only balanced at the cap however, players won't enjoy it at lower levels, won't play it and it detracts from your game.
Then there is an Achievable end game. So essentially, have a level cap, and have special stuff there. A game that doesn't do this well for example, is Maplestory. When I was playing no one was near the level cap- it was something like 255 and the closest was 178 after a few years of playing. Getting a level was several days worth /played time. At the same time, it can't be too easy. In Guild Wars, it is possible to get to the cap in a day of playing if you know the game well. However, another point is that you have to have something to hold onto your players at the cap. If I recall correctly, the DCUO Beta/Release had an excellent leveling system and it didn't take too long, but it was too quick either. But at the level cap there was barely any new content, and so players disliked the game. And even after a player goes through all of the content you have, you want to hold onto them, by interesting them in upgrades and other special or rare items, so gear, mounts achievements etc....
Finally, I have replayability on my list. Its probably the least important, because if done correctly, the player will never run out of things to do on their main and won't want to roll an alt. However, if they do choose to reroll because they dislike their character, or they want to get their friends a different role, the game has to be different enough from a second perspective that they will stay and push through the content again.
I'll probably start digging deeper into each of these, what tricks I would use, mechanics I would like to see, and all that. Comment if you have an idea or suggestion!