The Wizard is my favorite class in pretty much any game, so I've got a lot riding on this decision by Goblinworks. While I understand that an MMO game necessitates a magic system that is different from what is found in the tabletop rulebook, I hope they can find a way to keep things similar.
One of the most important things to me is the sheer number of spells. Magic allows for a lot of versatility for a wizard (and, some other types of casters). The core rules devote over 130 pages to the various types of spells. I would hate to see that reduced to the standard twenty-or-so spells per casting class that you find in other games.
Give me options! Give me a long list of available spells. And don't make them all available just by going to a trainer. Make me work/adventure/explore/fight/survive to acquire most of them. In fact, outside of some core spells at each spell level, I should have to go out in search of the rest.
Also, don't worry so much about balancing offensive power between various schools of magic. If I choose to specialize in Divination, so be it. As long as I am made aware of the drawbacks/benefits before doing so, let me choose to play that way without feeling like you have to add some crazy divination mind-bolts just in case some poor schlub was too dumb to plan ahead, decided to specialize in Divination and now complains about a lack of firepower.
Anyhow, back to the original topic - how to mimic the feel of the core rules without impeding the unique MMO gaming style. How about this -
A wizard gains an appropriate number of spell slots, much like in the core rules. So, let's say I've got the equivalent of a level 3 wizard (yes, I know there aren't supposed to be any levels, but that's why I said "equivalent"). This means my wizard can cast 4 cantrips, 2 first level spells, and 1 second level spell.
Instead of "Spells per Day", think of this as more of "Spells per Fight" or, to use more MMO nomenclature, "Spells per Pull."
Via my cool magic-user interface, I have the ability to change what spells I want to place in my "Spells per Fight" slots. I can go to my spellbook, which contains a great variety of spells, and select what I want to "memorize."
So, let's say I choose Resistance, Light and two instances of Acid Splash as my cantrips. Mage Armor and Burning Hands as my first level spells, and Blur as my second level spell.
My group, which is exploring some ancient ruins, enters its first fight (or first "pull"). Throughout the course of the fight, which takes a minute or two of real time, I burn through all of my spells. That means, if I go into the next fight without resting, then I won't have any spells to use... I'll be relying on my trusty crossbow or staff.
However, while everyone else is gobbling food or drinking liquids to regain lost hit points, I can also hit a nifty "study" button on my interface. My character whips out his spellbook and begins studying. Perhaps it takes twenty seconds to re-memorize all of my spells. Or, perhaps it's based on the number and level of spells that I am memorizing. Regardless, it's a mechanic that mimics the eating/drinking mechanic found in most MMOs. And, at the end of my twenty second wait, I've got a fresh slate of memorized spells that I can use for the next pull.
If, mid-way through the exploration of the ruins, I decide to switch my spell selection. That is easy enough to do via the interface, and then its just a matter of "studying" again. (Or, maybe there's a slight penalty of added time to change the spells that I am memorizing.)
If the party is getting tired of waiting on me. Well, that's either the cost of having a fireball-slinging super wizard in your group, OR I have to start rationing my spells a bit.
Either way, this would keep the spell management aspect of the core rules in the game, while not unduly inconveniencing the other players.
