I've heard this argument many times, and I totally understand it. The DnD spell memorisation system is great. For a DM who gets a lot of inspiration from literature, however, it's in some ways an odd choice. It's one of the singular systems amongst all literature, unique to its own setting. Like LeGuin's true-name system or Anthony's 'I-found-my-special-purpose' system, it's in a niche off to the side of the main body of literary wizardry. By far, the most widespread representation of wizardry in fantasy fiction is a spellcaster who knows certain spells, can cast them at will, but becomes fatigued in the process.
My answer to this, then, is to rely on the well-worn idea of spell points. In my games, these spell points definitely don't indicate some sort of mystical energy reserve, like mana (though that could be another potential niche system.) Rather, it's an abstract measure of the caster's mental wherewithal, much in the same way hit points are an abstract measure of a character's physical soundness.
Here is my posting on spell point rules from one of my online PbP games:
Wizard = Int + (Wis/2) + 1d6 per level
Cleric, Druid, Ranger = Wis + (Int/2) + 1d6 per level
Bard, Paladin, Sorcerer = Chr + (Wis/2) + 1d6 per level
Rather than the cast-and-forget magic system based on the books of Jack Vance, which every version of D&D uses to some extent, I found that this much more open system promoted more creative gameplay. Under a Vancian system, there are a lot of good spells that honestly just never get used since the circumstances where they might be more useful than something like a Fireball are rare enough that hardly anyone ever memorises them. I think this outweighs the 'interesting gameplay' factor of having to plan hours ahead for what spells you're likely to need for the day.
At first level, your spell point total is equal to your prime caster ability stat. In other words, Wisdom for clerics, Intelligence for mages, Charisma for a bard, etc. To that you add half your Constitution score. To that sum, you add half of your Wisdom score, unless it is your main casting stat, in which case you would add half your Intelligence.
Spell points are regained with complete rest, at the rate of 1 per hour.
Your 'main casting stat' is the one your class uses to determine whether you get bonus spells.
|The ability that governs bonus spells depends on what type of spellcaster your character is: Intelligence for wizards; Wisdom for clerics, druids, and rangers; and Charisma for bards, paladins, and sorcerers.|
If your bonus-spell-ability is high enough to get you bonus spells, this becomes bonus spellpoints instead. You add the number of points it would take to cast the bonus spells allowed for your level.
How many points does it take to cast a spell?
Here's a quick list:
Level 1: 1 point
Level 2: 3 pts
Level 3: 6 pts
Level 4: 10 pts
Level 5: 15 pts
Level 6: 21 pts
Level 7: 28 pts
Level 8: 36 pts
Level 9: 45 pts
As you can see, it's the points required to cast the previous level spell, plus points equal to the current spell's level. Mathematically, it's the additive cumulative of the spell's level.
At first level, and when you gain a caster level, you gain 1d6 spell points, plus the general modifier from your main casting stat.
After using this system for many years in both low-level and mid-level games, I'm very happy with the results. High level spells are a huge deal to use. Low level spells can be tossed about fairly freely, but my caster players soon learned that it added up quicker than they expected. Wizard cantrips are 1 point each, not free. Any caster has to study their spells or pray daily, or they begin losing their detail and become dangerous to cast. Cure Light Wounds is the only real game-changer here, but in play it has never come even close to making the stylistic difference in the game engendered by healing surges.
In the end, my players still choose to play fighters, and feel satisfied in doing so. Players still end up dead, too. But the experience of magic in the game gels much more closely with what the players saw in their imagination.
I'll go on in the future to detail a lot of the other magic systems my players have run into, including what my players always enjoyed as a great take on the Dying Earth system.