Actually, the problem is I think the switchover from 1e/2e to 3e.
From a post on wizards boards...the differences between a 3E and a 1e/2e wizard.
1. Ability Score
To begin with, there is no increase every 4 levels and to even be able to choose the wizard class, you needed a minimum INT of 9 while to be able to cast a spell, a wizard needed to have a minimum INT score equal to the spell level x2.
With the 4d6 rolling method, getting a score above 16 was extremely lucky and given that the Tome of Clear Thought (only magic item that could increase your score other than the ubiquitous WISH spell) could only be used once and it wasn't an item a player could create (I'll be getting back to magic items), many of the higher level spells didn't come into play into the campaign since a player wasn't likely to have the minimum intelligence.
There were also 2 other restrictions.
Restriction a) To learn a spell, a wizard had to roll under their % chance to learn a spell (base of 35% @ INT of 9 +5% per point of INT above 9). If unsuccessful, the player could not put it into their spell book UNTIL they increased in level and rolled again and had still access to the spell. (No using other people's spellbooks to get around this )
Restriction b There was a limit to how many spells one could have in their (ONLY) spellbook. Starting at a low of 6 @ INT 9 and ending at a high of 18 at an INT of 18 (no restriction at an INT of 19 and above). At a score of 16 (10% exp bonus) you could only have 11 spells per level in your spellbook.
At a glance, you can see ALREADY how the 3E wizard got a boost just from how INT interacts with their abilities (whereas the melee classes actually got significantly weaker as the explosion of the STR table really screwed them over)
The wizard class
With no bonus spells for INT AND a base spells per day that saw the following
a 1st level wizard only be able to cast 1 spell
while a 10th level wizard had 4 4 3 2 2 (no cantrips of course)
and a 20th level wizard has 5 5 5 5 5 4 3 3 2 even moreso than the 3E wizard, a 1e/2e wizard player had to husband his resources even more effectively.
However, there's one big issue that really allowed the 3E wizard to make out like a bandit.
Scroll creation in 3E is selectable at 1st level. In 1e/2e, scroll and potion creation was limited to 9th level and higher. (but, I'm still not ready to get to magic items so hold on )
The effect of such a draconian restriction meant that spells like Comprehend Languages and even Knock were rarely (ab)used since combined with PART 1 (INT), no sane mage would waste a precious spell slot on things like that (true in 3E as well, but scroll creation gives the 3E MU an easy reach around)
Furthermore, spell acquisiton was firmly under DM-control. Technically, the only difference between this method and 3e is that in 1e/2e, all magic using spells are off limits to the player unless the DM says otherwise whereas in 3E, all spells are fair game unless the DM says otherwise. A slight but IMPORTANT difference.
Our poor generalist wizard in 1e/2e would get 3d4 or up to his INT limit 1st level spells (which included read and detect magic) but would only get a new spell in 3 ways.
a) When they would acquire a new spell level, so basically once every other level, a generalist would get a new spell (specialists got one spell from their school every time they levelled)
b) Capturing a spellbook and this wasn't EASY (If you'll notice, in the thread detailing the classic adventure, the wizard doesn't get access to a spellbook until he's 4th level )
c) Spell Research.
Ah, good old spell research. You needed a fair amount of downtime (2 weeks per spell level and no interruption longer than a day otherwise you lost a week) and money (1d10 x 100gp) per spell level and you STILL had to succeed on a % spell chance roll.
d) Trade
If you're DM was lenient, you might find a friendly mentor/colleage that would trade one spell of the same level or lower for a spell of the same level. Otherwise, the cost of buying said spell was AT LEAST 1000 gp per spell level (DMs where well within their right to make that 10000gp per spell level).
Spells in Combat
While others have pointed out that fireball was king in 1e/2e, few have pointed out have well weak other spells were when compared to their 3e version.
The Initiative system in 3e was a HUGE boon to ALL spellcasters.
Previous to 3e/4e, initiative was rolled every round by the players and it was modified by either adding your weapon spell or adding your casting time (CT for wizard spells were almost always equal to their spell level while for priests it was spell level +3).
With a dagger having a WpnSpd of 2 and a Longsword a WpnSpd of 5, there was great incentive NOT to use the big gun spells. In magical combat, Magic missile was KING since with a CT of only 1, it would cause the other mage almost invariably to lose their spell as ANY damage taken from the beginng of the round to the their turn in the initiative order would cause the spell to be lost.
Then there's the fact that many of the spells actually got weaker as you increased in level. In 3e, as you increase in level, your likelihood to be affected by a spell that targets your weak save INCREASES which made many Save or Suck/Die spells that much more effective. Contrast this with the 1e/2e model where the effect of the spell was not modifiable by the caster yet the targets increase their likelihood of resisting the spell as they level.
Then there's the effect of many spells themselves. Many spells were actually DANGEROUS to the caster themselves. Casting spells like Permanency would have permanent (heh) effects on your character and nobody abused Po,ymprh/Shapechange/Teleport since the spells had such a horrendous drawback.
THE BIGGEST boost to the 3e wizard however was MAGIC ITEM CREATION.
I'll give a nice example....Staff of Fire (or as it was in 1e/2e, the wand of fire)
Pretty straightforward in 3e to create right?
Well, here's the 1e/2e equivalent as described in Spells & Magic
Use of the Contact other plane spell.
Requires 2 weeks and 400 gp just to learn how to create it.
Requires forging by a master smith of the Azer, from brass smelthed in the City of Brass, tempered by the fiery breath of an adult red dragon, inscribed using a blood red sapphire and then finally polished with a mixture containing the ash of a 1000 year old tree destroyed by fire.
Potion and Scroll creation wasn't as obscene but it sure as hell wasn't anywhere near as easy as 3E (had to be a 9th level wizard with access to a 10,000 laboratory)
With no easy spell items like scrolls and wands, a wizard player was truly limited to what he had memorized and what the DM was generous in giving out as treasure.
The advantage for the wizard was that spells like comprehend languages and Knock could be so effective since they were a limited and rare quantity. When 3E was created, the designer simply kept these effective spells without compensating for all the restrictions they have lifted from the wizard.
