Grumpy Gamer's Egregious Archetypes, Part One: Puny Humans
Role: The Generalist
Identifying Characteristics: Average everything, moustaches and beards not available to other races
Strengths: The standard build platform, ability to grow stylish facial hair
Weaknesses: Just about always the very least interesting race available.
Humans can be found more or less everywhere. Very few MMOs, regardless of genre or setting, don't have human player-characters, and some have more than one variation. Refreshingly, humans in MMOs are usually not limited to one particular ethnic or genetic stock, and often have as wide an assortment of skin tones and bone structures as humans in the real world. Racism in fantasy settings takes a different approach - why would anyone bother disparaging another human being when there are other entire species to hate on?
In games where race plays a role in class selection, humans often have the dubious advantage of having the most class options at character creation. In games where race doesn't limit class options, humans are just another hairdo, and are usually very vanilla compared to the other, more exotic species. They have a medium build, but may occasionally be the tallest race in settings without playable Orcs and/or more diminutive Elves. They typically have "flat" stats or attributes, with no inherent bonuses or penalties, but they often have little skill bonuses here and there to make up for the lack of genetic specialization.
In terms of personality, humans are also usually middle-ground milquetoast. Like Neo says, they are "just some guy," a persona that works fine with the Campbellian monomyth that most fantasy games are built around, but which doesn't start out as all that appealing. Typically, they serve as a sort of meter for the other races, because the other races are better at stuff than puny humans. They are aggressive, but not as aggressive as the war-like Orcs or other beast-man races. They are stubborn, but not as stubborn as Dwarves. They have a talent for magic, but the mystical magical Elves make them look like first-year students at Hogwarts. Even when humans are a plain and simple folk, they are overshadowed by plainer, simpler Hobbits. Humans are often awed by the ancient and mysterious powers of the elder races, while those elder races might be more blasÃ© about it even though they are all following the same "outsider newbie" narrative. The elder races are the ones that built the fantastic dungeons and ancient temples now fallen to ruin, and Humans are the ignorant, unruly children blundering through them, knocking over the lamps and smearing chocolate on the drapes.
As dull as they may be, humans are the most relatable species. Elves, Dwarves, Gnomes, Orcs and the others may be more exotic and entertaining, but they are also more alien and strange, and this doesn't always jibe well with some players. Not everyone wants to be a midget, a monster or an emo fop. And while they may not have the diamond-edged talent bonuses inherent in some other races, neither do need to make up for the brittle balance penalties that go with them.
In a way, this makes them the ideal proving ground for theorycrafters testing new character builds. Starting out with flat stats makes it a bit easier to track bell-curves and calculate per-point modifiers with diminishing returns. This doesn't really make them any more fun to play, but it is a small feather in their otherwise-bland hat.