Okay, I don't know why some people think that having to master a system in order to play something is ever a good thing. One of the many reasons I enjoy 4E is because all classes, regardless of their narrative capabilities, all follow the same mechanics for task resolution. This allows a player to learn one system and then be able to play any concept she desires from the options presented to her, instead of being forced to learn additional rules to play, I dunno, "privileged" vs. "newbie ghetto" classes I guess.
For example, I like wizards. In any given game where a spell-slinging pushover is up for grabs, I'm most certainly going to give it a shot. I did this in Advanced Dungeons & Dragons, I did it in Shadowrun (street mage), I did the Jedi shit in Star Wars (WEG version-only), and when 3E came out the first character I rolled was a sorcerer (mostly because I wanted to see how spontaneous casting actually worked out in play).
In no instance did the extraneous rules add anything to the class except for additional work on my part. Having to use other rules to do the stuff my class is purported to do did not make it "feel" more like magic, or whatever. I think this is a mental hangup for many, in that by dealing damage with a separate subset of rules makes it feel different than how the other guy does it. In the end its just damage: the description is really what sets it apart.
The fact that D&D wizards used to be wizards for about one combat encounter a day didnt help matters, either. -.-;
To make matters worse, as Wizards released more classes they also made new rules for many of those classes. Want to try out a new class? Be prepared to memorize even more rules!. I remember taking a lot of time to learn how meldshaping worked in Magic of Incarnum, and boy did no one want to give any of them a whirl even after I gave an abridged explanation of how it all worked.
Honestly, were any of these classes made more fun because of the secondary systems I had to learn?
No. Fuck no.
One of the reasons many new players don't want to try those classes is because of the extra work and mechanics you have to figure out in order to play them. Like, you learn how skills and mundane combat works (and that was annoying enough what with opportunity attacks and grappling), but woe to the player who wanted to try something with scaling damage dice. They bellied up to the table to play, damnit, not do homework.