Generally something that can lure people in and at the same time have a great friendly UI. Something I dislike is having a giant tutorial explain to me EVERYTHING right away at the beginning; I like to just go and do things while having some sort of small aide rather than outright "Do these before you can even hold a sword".
Once we're past that stage it's really dependent for me. I prefer something that holds replayability and reason for me to continue after I've done basically everything (sure that part is a LONG process, but honestly. there are games out there that die off once you hit top level).
Phantasy Star Online was surprisingly good for replayability. How? Weapons and Armor have distinctive values, making rare drops become hunted often so people can get that high% (stronger in regards to Phantasy Star)/ Weapons that go as far as requiring Specific character ID colors (randomized as you create one; dependent on the characters used in your name), playing on Ultimate (Level 80+), and having drops as steep as 1/2000 where you may only find 16 of those unique monsters during said hunt. The only downside was PSO probably has the worst exponential pacing as weapon choices don't really matter until Ultimate (Or Very Hard on Episode 4); making a lot of the rares found in Hard/Very Hard very janky items; usually used when you have nothing else stronger.
Runescape's replayability is almost non-existent, but honestly it really doesn't need it unless you've played the past 10 years and have done everything you can. It's definitely not the best out there, but it does things that most MMOs don't, and that's generally being able to play without engaging combat with any mobs for the majority if you wish to do so; WHILE progressing. Albeit it is an extreme grinderfest, it's still a decent stable MMO; very good for a Java platform and a browser based MMO.
So for a list, I'd go for...
- A progressive tutorial that isn't completely "in-your-face" and not mandatory to do everything before you are set free
- A way to make it long-lasting; most MMOs get people to level 50 then they are simply done with nothing else to really do
- Balanced combat mechanics; it's problematic when everyone is a warrior because they have no cons while the others have about 10
- "Something for all". Some like to PvM while others like to PvP; separate different worlds/servers so both sides (or more if they exist) can enjoy
- Relatively decent scaling so that you don't feel like you HAVE to grind to get anywhere, but not so fast you don't max out in a week... difficult to do earnestly.
- Lore... this one speaks for itself. You play an MMO, and you REALLY want to try to get into what's going on in terms of lore, but you also want to play ASAP. This is probably the hardest part for any MMO to do considering lore is outright ignored by the majority of players. It's only problematic because usually to progress, you need to know what the hell is going on, but at the same time you don't care because all you want to do is just beat it for reasons(lol Runescape). Though this part isn't entirely an MMO killer, it's something I find that seems to be ignored and barely tampered with, so players tend to not care and just move on
- Ranking system; this simply encourages some players to play all they can and try to reach top-scores. Even better when there's multiple categories as there's more space for players to reach to
- Economy balance; We ALL know how MMOs get when the player market gets stupid. There are usually solutions to this, but it depends on the game... Unfortunately my example of Phantasy Star Online is bad considering the private server I go on made the prices of everything ridiculous... costing some items 3000 Photon Drops (which are rare items dropped by any mob in Ultimate at a 1/125 rate. Considering it's a dungeon based game with limited amounts of mobs per session... you can see how this is bad)
- Frequent updates; by frequent, I mean maybe weekly (or if developers want to go all out, bi-weekly). The reasons are obvious enough. Fresh new content. Game-breaking fixes. Overall longer-lasting atmosphere to players old and new.
Just some things I could think of. But here's a big NO-NO for ANY MMO to ever commit. NEVER EVER make your MMO a Pay-to-win service. Even going as far as beneficial pay services can become a stretch to this. I know these games need to make $$$ somehow, but making players pay to advantage over others really deters a lot of people. Due to people simply being unable to utilize any e-services such as paypal or simply using a credit card (where most countries have a legal age requirement). I honestly think the best way to make money (as an MMO developer or manager or w/e) is to do what a lot of MOBAs have been doing. Offer 2 different in-game currencies; one purchased with cash and one you get for playing in-game and make premiums offered to both sides; with obvious discounts to those who purchase.
Last, but not least.. ENJOY THIS WALL OF TEXT NO ONE WILL READ.
