Bartle's MUD personalities was groundbreaking for its time, but as games evolved, the original personality types seem to have become less relevant due to convergence of playing styles. Nowadays games tend to blur the lines, so it can be very hard to tell say, an Achiever apart from a Killer in a PvP-oriented game with many PvP achievements/rewards.
I've seen a few new proposed spins on the theory, like one that assumes everyone is an Achiever by default since games are increasingly catering to and rewarding a variety of playing styles.
I also find that there is a lack of attention paid to co-op gameplay in Bartle's article, despite co-op being as much a part of multiplayer gameplay as competition. That's probably the biggest disconnect between the article's assumed environment and NWN. NWN servers seem to tend towards co-op gameplay, and I don't see a lot of servers encouraging PvP. There's also a lumping together of traits that may not be true, for example that Socializers make bad players - that's really not true, as I am about to explain:
I'd personally use different axes myself, drawing a little bit on psychology. One axis would be a social axis based on Horney's Neo-Freudian theory, i.e. with one end indicating tendency towards co-op, the other end being competitive and the middle being no effort to either move towards or against people. The other axis would be the Casual/Hardcore axis, representative of the depth of experience and desire to learn of the player with regard to the genre.
I'd also use 8 personalities to identify players by, based on D&D class naming conventions:
Pure Hardcore - "Wizards" - Loosely based on Bartle's Explorers, these players are more interested in experimenting with the game and gaining knowledge, with not much inclination towards or against players. Often the theorycrafters on places like ElitistJerks, but they rarely bother to make their findings digestible to the masses.
Hardcore/Co-op - "Bards" - These players have the same drive to excel as Wizards, but are more socially inclined. Maybe they like the feeling of being relied on, or being part of an effective team that gets things done. They also tend to play the loremaster role, being the most willing to share information in English out of all the Hardcore types. Just like Bards in an D&D, everyone wants one of them in their party.
Pure Co-op - "Clerics" - The bridge between casual and hardcore. They enjoy tagging along in a party and playing a supportive role because they like being around people. They may not be the ready source of information that Bards are, but they are generous in other ways, frequently giving out free items and buffs out of goodwill.
Casual/Co-Op - "Druids" - Druids like being around others, but they also like stopping and smelling the flowers. They also aren't quite as politically-inclined as the other Co-op types, treating the game, or at least its mechanics, with a level of detachment. The players on NWN RP servers that sit around in a tavern and chat all day are most usually Druids. Bartle's Socializers are probably closest to this group.
Pure Casual - "Rangers" - These are the lone rangers that travel the world and appreciate what it has to offer. Like Wizards, they channel a little bit of Explorer, but while the Wizards are more interested in the gears that run behind the world and make it tick, Rangers appreciate what the world offers on the surface.
Casual/Competitive - "Barbarians" - Barbarians come into the world to make a name for themselves, but lack sophistication. They are frequently seen trolling in chat, using pelvic thrust emotes behind female characters and other activity of the like to attract attention. This usually happens in the form of ire from just about every other group. But they get off on it anyway.
Pure Competitive - "Fighters" - Like Barbarians, Fighters want to make a name for themselves. Unlike Barbarians though, they are more inclined to do so through the system. So they are the duellers, the PKers and the powerlevellers, hanging around Arena and Action servers and doing what they do best - fighting. Be it other players to prove their strength or monsters to get shiny loot they can show off. Bartle's Achievers are probably closest to this group.
Hardcore/Competitive - "Assassins" - Like the other Competitive types, Assassins are here to make a name for themselves, but like other Hardcore types, they care more about achievements beyond those defined by the game's shiny titles and rewards. They don't share their secrets as much as they share their exploits. This makes them the most likely group to post time attacks or videos of them soloing entire parties in PvP and winning on Youtube. Bartle's Killers probably fall under this.
And this is what I meant when I said the co-op aspect was underdeveloped. Three of Bartle's four personality types fall under the Hardcore/Competitive quadrant, and the entire co-op and casual demographic was represented by Socializers.
But this is not a flaw in Bartle's original idea. Video game profileration has skyrocketed since 1996, and demographics have become more diverse. There's been a large increase in female players, and cultural gender roles suggest that they tend towards co-op gameplay. Also, with games becoming mainstream, casual players are increasingly outnumbering hardcore. With NWN more closely resembling a mainstream graphical game than a text-based MUD, Bartle's definitely needs some kind of updating for use in NWN's context.
