Whether it's an MMO or a single player game, there are just some things I wish all developers would take in to account. Mind you this blog post is totally just my opinions on the subject and I have no formal expertise in the area, but I wanted to just put them out into cyberspace for the hell of it. In this day and age of both technological advancement and player expectations these are some things I'd like to highlight.
1 Character Customization: OPTIONS OPTIONS OPTIONS! A robust character creation and customization system is vital for any RPG. Players become more invested in a character that fits as closely to their imaginings as possible. If you're going to make an RPG make sure the player has plenty of options both at creation and later during play. Creation options should start with an attractive baseline with plenty of face and body sliders to tweak, a variety of textures for complexion and numerous hair style options that hopefully don't look like shiny plastic. Game play customization should include the ability to modify the appearance of gear preferably both in form and color so the player can create a look that truly exemplifies their character concept. Games that generally do this right include: City of Heroes, Aion, Neverwinter Nights
2. Voice Protagonist: Yay or Nay? Most likely nay. Why? Because unless you're going to invest in enough voice actors to provide 3 to 5 different voices for each gender for EVERY DIALOGUE option in the game that your protagonist can choose, then you run the risk of causing a disconnect between the player and their character by virtue of the voice just not sounding right with the appearance the player has chosen. Voice acting is expensive and paying multiple actors to do protagonist dialogues would probably break the budget allotted for the game. If a company could make such an investment I'd say go for it. Most RPG's are very story driven and involve numerous dialogue interactions between the player and various NPC's. Non voiced protagonists typically have a few voice options at creation simply for combat and interaction audio. Games that generally do this right include: Dragon Age: Origins, Aion, Neverwinter Nights
3. Reality in my fantasy. There's much leeway given for RPG's as far as ignoring certain elements of reality. More so if it's a game set in the fantasy genre. That said there's a need for some measure of reality to make the world live. Water should never be "out of bounds". It smacks of laziness and taking a cheap shortcut. If water isn't out of bounds then water needs to react to player input both with visual and audio responses and for the love of all creation please add swimming physics and animations. Even if nothing in your game hinges on underwater environments, nothing is more jarring than hitting an invisible wall because you reached the shore of a lake or if there are no barriers you simply walk under the surface of the water along the floor of the water body. Include weather too! A world that feels alive has varying stages of day/night and weather that changes. Games that generally do this right include: World of Warcraft, Rift, Elder Scrolls: Skyrim
4. Romance! While difficult to do properly in an MMO, many ground breaking single player games have done wonderful jobs with romance options. If you're going to include romances then a good romance should tell a smaller but engaging story of the player and their romantic interest within the greater story of the game. The romance should start subtly and grow at a natural pace through player interaction with the npc and the decisions the player makes throughout the game. Romances should also be broadly inclusive. While it may be unrealistic to some, people have varying tastes, and restricting romances to specific genders often leaves many unable to enjoy the option they would have preferred. MMO's don't often have NPC's that are with your character through the bulk of their story and indeed the story of an MMO is an ongoing thing. This makes developing a romance difficult (but not impossible as Star Wars: The Old Republic proves) in an MMO. That said I feel it is better to have a small selection of romance-able options rather than making any NPC a potential mate. The game Skyrim allows you to marry most NPC's you meet but has no real story development of a relationship. Games that generally do this right include: Dragon Age: Origins, Dragon Age 2, Baldur's Gate 2, Neverwinter Nights: Hordes of the Underdark
I know my selection of games is a bit limited in my examples but these are games I am intimately familiar with and offer (in varying degrees of success) the things I outline above. Ultimately the ideal to have the player bond with their avatar in the game and to truly connect them to the world and environment. If you can do that then you've got a loyal customer, either as a subscriber to your MMO or a repeat purchaser of your expansions/DLC and future games.