Fanaelialae
Legend
I'm not fond of Vancian casting, but honestly, I haven't seen a magic system that I felt was really better.
Spell point/mana systems have the same problem as psionics did - blowing all your points on big spells or getting abilities that let you "overpower" your abilities.
The At-Will/Encounter/Daily of 4E suffered from the fact you couldn't throw 2 fireballs in the same combat if you wanted, and it was the game designers who got to choose what was an encounter ability and what was daily - and thus adjudicate it's power.
I'd like to see 5E return to a form of Vancian casting, but have some options for recovering low-level spells more rapidly. I'm not fond of Pathfinder's "cast cantrips forever" spamablity, but a wizard casting (a single) magic missile every other round wouldn't bother me.
Another interesting option might be a build-up mechanic - a wizard could blast away continuously with a minor spell, but each round he uses no (or a minor fraction) of magic perhaps he could build up to a more powerful spell.
Of course, I'm probably also unusual in that I want to see the wizard using mundane weapons on occasion - whether a dagger, crossbow or quarterstaff.
I wonder if there might be some appeal in balancing AW/E/D around increased flexibility. Something like, every spell has 3 versions, one for each level of frequency. You have x spell slots, but you can choose to memorize any combination of spells. You could memorize x at-wills, x encounters, x dailies, or some combination thereof. 3 options might be overkill, but even if you dropped it to just at-wills and dailies I could still see it working.
For example, Invisibility. The at-will version might only last until your next turn (1 round), while the daily version might last for an entire encounter (5 minutes). If there's an encounter version, it would be somewhere between those options. That's just an example of course; the standard could instead be that at wills last for rounds, encounters last for minutes, and dailies last for hours. Either way, those are just fiddly details.
So, if you had 5 spell slots, you could memorize at-will Invisibility and 4 other spells, or Daily Invisibility five times, or some combination thereof. It might be a reasonable compromise between the various editions, and it would allow players to play their casters as they prefer. Like the 3e warlock, memorize at will versions of spells. Like the 3e wizard, memorize dailies exclusively. Like 4e casters, take your preferred combination of frequencies.