If someone doesn't like what you like that means they're immature?
ROFL.
I don't think the word "mature" means what you think it means.
4th Edition is a fundamentally different game than previous editions of D&D. It doesn't scratch many of the same itches. It doesn't even try to. If those particular itches weren't important to you, then 4th Edition may be preferable. But if those itches are important, then 4th Edition isn't going to work.
In the case of the player who prefers 3rd Edition wizards, the itch he's looking for is character customization. Pre-3rd Edition, wizards were basically the customizable classes. 3rd Edition opened up the customization of other classes, but lots of old school wizard players just kept right on playing wizards (which remained the most customizable class -- particularly in terms of their ability to customize to different situations on different days).
In 4th Edition, customization has been drastically curtailed. There are fewer options and the options are all very similar to each other. This is theoretically great for balance (although in practice 4th Edition appears to be just as broken and unbalanced as 3rd Edition was), but if you play roleplaying games because you enjoy tinkering with your characters... Well, the game you enjoy playing has been severely castrated.
One of my personal bugaboos is the relationship between the game world and the game rules. My preference is for all action to be born out of the game world. I "translate" that action into the system and use the system to resolve the action. I want the mechanical aspects of the system to be smooth, effective, accurate, and fun -- but I still consider them to be in service to the world and not vice versa.
4th Edition not only turns that on its head, it frequently says, "




the game world. The game world doesn't matter. The mechanics do what the mechanics do."
And, again: If these things weren't important to you, you probably don't miss them. You probably don't even understand the problem.
Here's an analogy: You take someone who loves football and you tell them they have to play baseball instead. They object.
"What are you talking about?" you say. "It's still a sport! It's still played with a ball! There are still teams! You still keep score! The team with the most points at the end of the game still wins! It's played in a stadium! The players wear uniforms! It's still broadcast on television! There are still play-by-play announcers! Concessions are still sold in the stands!"
That's all true. But baseball isn't football.
And, for me, 4th Edition isn't D&D. I don't care what name is printed on the front cover. It isn't the game I've been playing since 1989.