One of the biggest criticisms I've seen of D&D is its Vancian magic system. The concept of a magic-user that has to memorize spells and can only cast a limited amount per day until he has rested and studied his spell book again. There are many who attack it as being too limited and requiring adventurers to leave the "dungeon" too prematurely and often to rest and recover. D&D 4th edition did a lot to try and fix the "problem" by letting players fire off low level spells as often as they wanted. It seems many wanted things to be more "fair "so they could to be like a Jedi shooting off their powers left and right just like a fighter.
I would at least agree that, on paper, all of these old-school spell limitations sound pretty lame and limiting. And I can certainly sympathize with someone who would want to change it if they didn't understand the mindset of the system. First of all, trying to play with Vancian magic in a rules-heavy system like 3rd or 4th edition isn't going to work well. These are games designed for "encounters", a painfully derivative word that has come to mean, "interesting things that happen" (as if nothing else in the game is all that interesting and therefore undeserving of a title).
In an encounter-based game you're not thinking about the big picture. You're thinking about spaces to do "stuff" in, while the rest is sort of filler that needs getting out as quickly as possible. In classic D&D, avoiding monsters and these "encounters" was actually more important and rewarding. In classic D&D you're not supposed to run into the room with the dragon with swords drawn and blazing fireballs, you're supposed to find a way to get the treasure while avoiding the fight altogether. You're supposed to outwit the dragon, not necessarily kill the dragon. Afterall, the XP gained by killing the dragon was peanuts compared to the XP gained from a dragon's treasure hoard (where classic D&D rewarded XP based on gold piece value).
Killing mobs to get loot is so ingrained in peoples' minds these days from video games and superhero films, that it seems almost absurd to play an RPG of any kind where you're not doing just that. It's hard for non-classic players to really understand this concept even if you try to explain it to them. The level 1 magic user, with his one-use light spell becomes extremely important when a confrontation with a monster actually does happen. The key here, and a running theme throughout classic D&D, was player cunning and wit, not sword and spell, overcoming challenges. A classic player's character wasn't going to come out of a session alive if he didn't do or think of something pretty darn cool and out-of-the-box during the session. That is something that has been lost in modern D&D where brute force, and less thinking, has become the rule of the day.
That's not to say you can't tinker with magic in classic D&D to make it more interesting. Other than a magic-user's wit and intelligence (which I'm not downplaying at all), he literally has nothing else to rely on during those early levels (where most characters live and die anyway). I want to make these classes more interesting and more dynamic to play. A house rule that I have been using in my latest campaign is for my players, an Elf and a Cleric, to be able to use their magic as a sort of fountain of power, rather than a one-shot blast.
The original house-rule I borrowed from someone else is to allow players to cast very minor versions of their spells for free. So a magic-user could light his pipe or even start fire with his Fireball spell. With Light, you could use it to send some "morse-code" styled signals. Etc.
My version of this house rule actually takes it a little further. I keep a mental note of how much of a spell is being used throughout the day and to what degree. Again, in the fireball example above, a player could decide to use his ability to "spark" some kindling perhaps 5-10 times a day, or instantly create a roaring fire for 1/2 the cost of a normal fireball. It will require some creativity to determine just what you could do in a minor fashion for some of the spells. I still haven't figured out how floating disc could be useful. But a clever player could probably surprise me in the right situation.
In any case, the player is spending his magic energy pool in creative ways that count toward his spell limit that day. I don't keep any hard rules for this, I just make a note in my head of how much he's used of his spell. Yeah, I know this is like a "mana" pool for each spell use, and some grognards may think that's heresy, but I personally believe this hybrid system fits even better with Appendix N than what we got.
My main source for this comes from Gandalf, but you could find a lot of other examples as well in D&D-inspired literature. Either because he likes being clever and subtle, or the physical drain is too much, very rarely do you see his full magical power being used. Instead, he's constantly being creative with his magic to scare or fool the bad guys. You can also see his weariness after using his magic, or in greater degree (eg holding the door shut from the Balrog and his encounter with the witch king) I like this approach more than the "bazooka wizard", that nukes everything in sight. And I feel it has a lot of old-school flavor. Magic-users can be far more versatile and creative and will never feel like they are useless after their spells have been used up after five minutes of adventuring.
Players will need to weigh the pros and cons to using their magic in one big shot, or in a lot of minor ways. Using your magic to start the fire this morning means that you're going to be in a world of hurt when you face a group of zombies later that day. Overall, though, this gives magic users far more options and freedom, something I think defines classic Dungeons and Dragons.