Spellcasting in d20 bugs me for a number of reasons:
- Spell knowledge is all-or-nothing. If you know a spell, you can cast it without error. If you don’t know a spell, you just can’t cast it. There is no looking up spells you don’t know in ancient grimoires. Moreover, you can’t be in the process of learning a spell and attempt to cast it even though you probably ought not do so.
- Following up on the last point, you know all of your spells equally well (unless you take a feat to specialize in a school of magic or something).
- It is entirely possible for a high-level sorcerer (or wizard, but sorcerer is more likely) to have a high-level spell of a particular type (a fire spell, say… or a powerful illusion spell) without having any lower level spells of that type. You can cast Meteor Storm, but not Fireball, Delayed Blast Fireball, Flaming Sphere, Scorching Ray, or even Burning Hands? You can cast Monster Summoning IX, but none of I-VIII? How much sense does that make?
- The whole memorize-and-forget thing is dumb.
- Metamagic is cool, but marginalized. It requires a serious investment in feats, as well as (in general) advanced planning. It was obviously a subsystem that was tacked onto a pre-existing magic system. Why isn’t it integrated? Why can’t spells be adapted in various ways on the fly?
Random, rambling thoughts towards fixing these things:
- Spell use is skill-based. A roll is required. For well-known spells, failure on the roll may not mean failure to cast the spell. It might simply mean that it is cast at a lower caster level or somesuch. A roll, however, allows DCs to be set for things such as applying metamagic.
- Spells are grouped. There might be an “Evoke Fire” group that has Burning Hands, Scorching Ray, Fireball, etc. in it – as well as metamagic versions of those spells. Knowing a spell in that group will make it easier to cast other spells in that group that you don’t know well. It will also allow some improvisation within that group. Improvisation might be more of a sorcerer thing than a wizard thing. Sorcerers are naturals – Wizards learn by rote.
- Ritual spellcasting – find something in a musty old book? Well… you can make a casting check to attempt to cast the spell as a ritual, even if it isn’t a spell you could normally cast. Look at the Incantation rules in Unearthed Arcana for inspiration. This should be more a wizard thing than a sorcerer thing.
- Spells will be classed something like unknown, familiar, and known.
- With a casting check and rules for learning spells, do I need a spells/day limit? What if subsequent castings of different spells of similar difficulty impose a penalty?
- Casting a spell at a lower caster level should lower the difficulty. I have no problem with a twelfth level wizard tossing 5d6 Lightning Bolts all day long.