Classes, as enticing as trying to piece together a game without classes seems. I must admit I don't think I'd trust my ability to create a desirable balanced system alone without a backbone like classes.
Down to it I'm only thinking of implementing 3 classes. It doesn't sound like much, but if needed it can of coarse be expanded. Of coarse after this explanation, I wonder if any more would even be needed.
Basically I'm thinking that each class will simply be given a large number of abilities and bonuses with themes. (currently only 3 per class planned) Each of the abilities and bonuses may have prerequisites, however none of them will require another ability. Each level a character will be given points to spend between these abilities and bonus. One point in an ability gives you the ability, then after that additional levels of the abilities will require additional prerequisites such as level and increase the ability generally. Each ability will also have modifiers, probably about 2 each (not finalized) that will boost particular parts. Bonuses will follow the same theory, except for the modifiers, and they may not have requirements to increase.
This way, anyone in the realm of warrior can put points into Berserker abilities, Defender abilities or Inspirant abilities at every level. However, due to the innate bonus' and traits of each ability it's likely more useful to stick to one or the other.
Trouble right now is, how to come up with enough abilities that are unique and interesting. Easy for casters, working on the warriors and theif types.