Nearly everything about the D&D magic system has been criticized at one point or another, but the two most common complaints in my experience are that the "Vancian" spell slot system makes no sense and that low-level magic-users are too weak and nothing at all like their literary/mythological counterparts. Unsurprisingly, I don't think either criticism holds much weight, particularly the latter one, but then I'm an unrepentant Dungeons & Dragons apologist, so what else would I say? However, I've had this idea in my brain for quite a few years now that could, if done correctly, introduce a neat little wrinkle to spell memorization that'd go some way toward addressing both criticisms -- or at least would make D&D magic a little less bland.
As I've long imagined it, a spell formula, the thing a magic-user spends time "memorizing" each day, is a means of temporarily "re-wiring" one's brain to act as a "circuit" for magical energies that are shaped by this to produced certain effects when "triggered." Once a spell is cast, the re-wiring associated with it is undone and that part of the magic-user's brain returns to normal. Where there's potential for adding some flavor is in imagining that, beyond the spell effect produced by memorizing a particular spell, the magic-user also gains some small benefit before the spell is cast. This benefit is a side effect of the cerebral re-wiring associated with the spell and is active only until the magic-user casts the spell associated with it.
For example, suppose a magic-user memorizes the 1st-level spell charm person. While memorized, the character temporarily gains +1 Charisma for the purposes of reaction adjustment and retainer morale. Meanwhile, a magic-user who memorizes the 2nd-level spell levitate gains the temporary ability to "float" a very short distance above the ground -- not enough to avoid pit traps or other ground-based obstacles but enough to give the character an eerie look to their movement.
That's the kind of thing I have in mind here. The trick, of course, is to find useful/interesting benefits for each spell that neither overshadow nor replicate the spell itself. That's going to be hard in some case, like read magic or read languages, whose use is so straightforward that I simply can't imagine what kind of benefit might be associated with having these spells memorized. The other trick, too, is to make the benefits good enough that the player of a magic-user might conceivably think twice about whether he should cast the memorized spell or keep it memorized in order to continue to receive its benefit.
Anyway, this is just an idea I've had for a while that I've never developed fully, so, if anyone wants to run with it, feel free. I'd love to see every spell in the LBBs have a benefit associated with it. Done right, this approach might go a long way toward giving low-level MUs a little more oomph without going to ridiculous extremes and encourage the memorization of certain less popular spells, owing to the benefits they accrue while memorized. That's the theory anyway; I'm sure someone will soon explain why this is a terrible idea.