The truth is, 3E was a pretty big improvement over 2E, it's just that it was designed in such a way that a lot of flawed mechanics really began to shine through with time, and in certain circumstances.
They made skills matter more, instead of just being proficient or non-proficient, which was a nice step. However, the skill system could really get out of hand and create situations where difficulty levels would always be set up so that someone who didn't specialize in a skill had absolutely no chance of succeeding in something, or it was trivial to the person who did specialize. Saving throws were similar to skills in that regard (though I don't think that really changed a lot from 2E).
Wizards got an improvement in 3E, in the form of extra Level 0 spells, and allowing wizards equal ground with their Int bonus as clerics got with their Wisdom Bonus. However, when a Cleric runs out of spells, they still can wear Plate Armor, and they can still be more effective with a weapon. The wizard quickly became useless. Though to 3E's credit, they did give Wizard the option of crafting wands and scrolls so that they could still be useful (at the cost of XP), however since all classes leveled at the same rate, it wasn't like it was any worse than 2E's higher XP requirements for Wizards.
The former long-standing philosophy of D&D design was that Wizards should be very vulnerable to make up for their great power later. 4th Edition is the first edition to re-evaluate that and realize that the problem is that it makes being a caster at lower levels to be frustrating, and being anything other than a spellcaster at higher levels disappointing.
My biggest worry about 4E is that they may have taken the former versatility from the Magic User away. However, I have to remind myself how little anyone else had. Perhaps I must concede that it's for the best for everyone's fun to spread around abilities to the entire party.