Something that really irritates me, and had me stumped for the longest time in the development of my own roleplaying system was the issue of classes.
Specifically, how many should there be? What differences should they have? How much customization should they have? And so on.
Most people who have played D&D for any length of time seperate it down into four classes, who, at their core, are seperate and irredeemably different than each other. They usually name Fighter, Rogue, Wizard, and Cleric, letting such friviolities as Hexblade, Samurai, Barbarian, and the like out to rot, as some sort of combination of those few.
Putting the calls of "bullshit! bullshit!" away, let's look at the reasoning for these classes. Surely, there is a good reason for fighter to be there. After all, he's the big tough guy, the one who get slapped upside the head and takes all sorts of pain so the squishier guys can shoot their spells and whatever else. The theif, on the other hand, deals with locks and traps so that the party can steal better, so that everybody gets less arrows shot into them. The cleric, obviously, exists to patch the party back up, and to provide both frontline combat ability and some assistance through his magic. And the Wizard, dear wizard, he exists to fling fireballs and make everybody fly and whatever else he decides to do.
And it's all flawed.
The main flaw is that the roles are reduplicated, or in some cases entirely unnecessary. The biggest example is the theif, of course. Why the theif? Well, think about it. The theif is a character who is a relatively inept warrior whose entire purpose is to steal things and get away with it. He relies upon fighters to save his hide from the physical problems, and the wizard to help him escape from the magical ones. In short, he's a fighter minus the fighting. A warrior without the war. And why?
It's entirely possible to have a fighter who is also a theif, a man who is capable of intelligent thought and disarming traps and stealing things, who is also able to put on some armor and slash through some people. It's called a hero, this amazing man. It's a hero in the very most classical sense, ranging back to the greek Oddyseus, or possibly even the sumerian Gilgamesh.
In the systems I'd always come up with, there were basically two roles, one for each way of solving things. If you solved things with blades and muscles, then you were basically a fighter. If you were a sneaky fighter, then you were a sneaky fighter. If you used bows, then you were a fighter who preferred to be called an archer, or whatever. If you solved problems with the powers of your god or gods or arcane formulas or demon-pacts, or any other sort of mystical and magical powers, then you were a sorcerer. If you were a holy man, you're still a sorcerer. The rules didn't care about the flavor, only your abilities.
That, to me, is how a system should be. It should be rules-light, with no rules for anything other than combat. Already I can see people asking why, people telling me why rules need to be thick and heavy to cover every possible situation and how we need skills covering things like diplomacy and social skills and not putting your elbows on the table and all that "fun" stuff. That's a topic for a different post, and I promise I'll go into it then.