If you have ever played an RPG, or for that matter any game that said it had "RPG qualities" or any sort of character progression, it's imperative that the player has some sort of influence on how their character works. Many games will give you a huge map of abilities, equipment, and other ways to tweak and personalize your play style and role while others will restrict you to a certain class. But those are just the two extreme ends of a rather bigger scale, most games fit somewhere in the middle by combining elements such as a class system with individual skill trees and more diverse equipment sets so a player can make a more unique character.
I have compiled a general assessment on the level of freedom a game allows to shape a character or play style on a scale of 1 to 5, 1 being no freedom whatsoever and 5 being complete, unrestricted customization.
1 - Static Characters
A 1 on the scale means little to no player influence on a character's abilities, armor, statistics, ect. Instead the player is given a static character and it's up to the player to use that character's given abilities in the way he or she chooses. While these games do have some form of progression such as finding different items or weapons, the character's outcome will still be the same. A few examples of this are traditional shooters, platformers, adventure games, fighting games ect. While this isn't necessarily a bad thing, as it provides a more controlled environment so that developers do not have to be concerned on balancing different character builds and eliminating possible exploits. The Legend of Zelda series is a notable example of this, you are given a character with a linear progression by collecting weapons and items, but it's up to the player to decide how they use these items that makes the game entertaining. This model may be successful in single player games, in MMOs this is a bad idea.
2 - Minor Character Options
Some games will give you static characters, but will offer some tweaks such as various equipment items or optional abilities that can provide a player some influence. Most RPG's that have strict character classes use this model by providing an extensive array of equipment that can somewhat adjust a character's statistics, however it may not be entirely enough to completely change the direction the character was intended to go. Examples of this are Team Fortress 2, which allow you to change weapons to tweak your playstyle while still retaining the main purpose of the game's classes. An example of this in a BYOND game would be pre-v1.52 NEStalgia, which provided a large array of equipment to influence your character as well as optional abilities, but despite this it still used rather strict classes. Casual Quest would also fall under this scale.
3 - Greater Character Options
Similar to the previous model, but with much more flexibility. This is usually a model that includes archetypes along with more diverse equipment, ability trees, and/ or direct influence over a character's stats. This also includes a game that provides various options, but still does not deviate or doesn't do much to the main play style. This model best describes what post-v1.52 NEStalgia is like now. WoW or LoL would also be considered a 3 on the scale.
4 - Freelance Character Customization
Games like this usually abandon archetypes to give the player a great array of options to build a character. This model gives a player building blocks to create their own unique builds, but still has some restrictions but they are very few. A game can still have archetypes and be considered a 4 on the scale as long as they are flexible enough. Rift is a good example of this, a character can "equip" 3 different individual skill trees to make a unique character for themselves. An example of a BYOND game that uses this model is Stolen Lands: While it uses classes to determine your skills, you can also learn some skills of a different class as well as have full control of stat distribution and equipment.
5 - Complete Free Form Character Building
This model gives the player complete control of their character in great detail and with little to no restrictions. The player is given a buffet of options and they can pick and choose whatever combination to fill their plates. This is the usual model for sandbox styled games such as the Fallout or Elder scrolls series. Sadly this model is rather rare in MMOs as it's a statistical nightmare to try and balance every character possibility and remove any exploitative or overpowered builds, especially in competitive game play.