I'm writing this as a response to a poll on the forums 'Skill based or level based in YOUR dream MMO'. I was (apparently) the only one to vote for a level-class based system. So I'm going to explain my choice here. Why would one rather have fixed classes than a freeform skill-based system? http://mmorpg.com/discussion2.cfm/thread/158770
The first reason is because it gives the player a clear role in group PvE and in PvP. I think grouping is generally less chaotic and more fun when everyone has a role. These roles can be very diverse and different in each situation, not necessary the holy trinity of tank-healer-dps. In PvP a class-system is good because you have to think of a different strategy against every class.
The next thing is that developers are much more free to add unique and powerful abilities to one class, without having to fear that everyone will have this ability within a week. Classes tend to be generally more unique gameplay-wise than what is possible with a skill-based system.
The next point is something that is important mainly from a roleplaying perspective, but that I find also imprtant even if i'm not a RPer. In a skill-based system, it is very difficult to make a character that has a clear style, like for example a priest or a thief, if you also want your character to be competitive. Let me give an example: you're roleplaying a priest in a skill-based game but for soloing, it would be great to have a fireball spell. That is however very un-priest-ish. So you have a dilemma: RP or being competitive? No such problems in a class-based system.
However, I agree with you if you say it is very dull to stick with a pre-made class for your entire career in a game. That's why I've worked out an idea, a sort of combination between class and skill. Call it 'create your own class'. When you first create your character, you would only choose a combat style for your character: things like 'priest of the light', 'frozen mage', 'wolfbrother', 'blademaster', ... spring in mind. There would have to be a lot of choices here. Based on your choice, you will be given a few basic skills. These skills shouldn't be very different from each other, apart from the grafical effect. When you reach a certain point in the game, you would be given the choice for your primary combat role. These are things like tank, healer, ranged damage, melee damage, support, ... Maybe some choices shouldn't be allowed for some combat styles, but everyone should have a lot of choice here also. Everyone who chooses the same combat role, will recieve very similar abilities, regardless of combat style. However, they would have different names and grafical effects. Then, later on, you would also choose two or three secondary combat roles. These could be things like pets, buffs, dispels, first aid, ... Both primary and secondary roles can be changed by paying an amount of experience. So what would the result be? You have a self-made class, yet all abilities are tied together by a combat style.
While writing this up, I realised this is a lot like the character creation in CoH/V, which I liked a lot, but the rest of the game was nothing for my taste.
Thank you all for reading this, and please let me know what you think about it.