Although ultimately I'm asking this question with regard to my specific online system, I'm hoping to get a sense of the pros and cons from other perspectives: free-form magic or rigid system?
There are probably multiple levels at which we could apply this discintion, so here are a few:
Spell levels: yes or no?
Caster level: yes or no?
Spell lists: yes or no?
Spells: yes or no?
D&D is an excellent example of a rigid magic system: 2nd edition (my favorite version) clearly uses spell level, caster level, spell lists, and spells with set effects.
Mage is an example of a more free-form magic system that lacks (at least) true spells and spell lists.
Numerous card-based games apply no true caster levels. If you have the card, you can cast the spell.
So overall, I'm trying to find a nice blend that works quickly, with little bookkeeping, but yet is fun. Rigidity tends to make things simpler for bookkeeping. Freeform tends to make things simpler in terms of not having to look up effects and such.
So what are your thoughts? What seems to work? What seems not to work? What are your presonal preferences?