The nice thing about gaming systems like Dungeons and Dragons is that unless you’re completely inept or putting a conscious effort into building a powerful character, odds are that everyone in the party will be around the same power level. What any player can and can’t do is carefully determined by combinations of stats, skills, feats, and other special abilities. If one member of the party decides they want to cause problems for everyone else, it’s usually easy enough for the rest of the group to show them their place.
Freeform games (especially online ones), on the other hand, are a horse of a different color. When you let everyone play exactly what they want to play, things tend to get out of control quickly. Yet in the midst of the chaos, somewhere between the point where reason falls apart and the one where rage-fueled indignation begins, you can get a keen insight on just what kinds of players everyone is.
The Overlord: Some people just really want to be the villain. They want to ride skeletal dragons, blight the land with evil spells, and wear crowns made of the severed hands of paladins. Consequently, these people still want to be an active part of the game, which usually means they never do anything that actively evil. The Overlord is usually more of an Indecisive Skeletor.
The Benevolent God: The evil Overlord’s good counterpart. He’s all knowing, all powerful, and wants to be your best friend/spiritual guide/Gandalf. He’s usually played by the worst role player in the group (or at least the one that is most deluded about their own prowess).
The Manual Monster: He really wishes he were playing D&D. Rather than using the complete lack of rules as a springboard for a unique and interesting character concept, he will choose a class and alignment, then complain when everyone else does things that differ from the game system standard.
The Special Flower: Probably the least unique role play archetype. Usually appears human but actually has come kind of fairy/demon/dragon ancestry that gives her special powers. Typically a woman with pale skin, long dark hair, and twenty different adjectives to describe her eye color.
The Kid: He’s the weakest member of the party and wants to make sure everyone knows it. He also wants to be best friends with everyone regardless of how little sense it makes to be both the apprentice of the Benevolent God and the bridge partner of the Overlord.
The Oddball: This person is the reason your party may include a flying jellyfish sociologist that plays badminton and communicates through charades.