- Clerics -- have a subsystem for turn undead; use spells, but unlike the magic-user, do not have to deal with memorization, or spellbooks
- Magic-User -- they have spells; a memorization subsystem; rules for scribing spells in their spell book
- Thief -- backstab; all the percentage-based rules for thief skills (hide in shadows, climb walls)
- Fighter -- ???
AD&D is a class system and indeed, each class (fighter excepted) brings its own subsystems to the game. Rangers and Paladins are more interesting than fighters because they have more systems to play with. In some ways, I think skill-based systems have a harder time creating character differentiation. Sure, characters buy different skills and thus, their characters are different, but the mechanics used are very often the same, just applicable at different times in the game.
I am not really giving Traveller enough credit; not all skill use is so monotonous. Traveller has several subsystems where the character's skills allow them to interact with the game -- starships and commerce being two of them. The advanced books like Mercenary and High Guard added even more subsystems. Nonetheless, the basic game does suffer from characters feeling samey and I think a lot of that has to do with the lack of subsystems.
My mention of Traveller stems from a conversation I had yesterday with my friend, Phil. We were discussing Traveller and came to the conclusion that even though it held a special nostalgic place in our hearts, it hadn't aged well, even considering the relatively recent Mongoose re-release. Why was that?
In short, D&D 3.x spoiled us with FEATS.
Feats solve a lot of the differentiation issues suffered by earlier rpgs. Each feat is a mini set of rules (or ways to break the rules) that can be used by that particular character. Fighters get tons of feats and so now, finally, after numerous editions, fighters get their own little subsystem and can break the rules just like the wizards can.
(Of course, mages and rogues get feats too, but it is obvious due to the fact that most feats are combat-oriented and fighters get so darn many of them, that fighters are meant to be the "feat-guy". Much like mages are "spell-guys" and rogues are "skill-guys".)
Feats also act as a means of differentiating combatants and creating combat styles and builds. One fighter might build to be the "trip guy", taking feats that allow him to trip his opponent. Another fighter can build to be a two-weapon fighter. Another can build to be great with bows. Feats give us mechanical ways, besides just a boring +1, to specialize with a weapon or a set of maneuvers.
This is one reason I find it hard to get back into some of my older games. I fantasize about giving Traveller, Rolemaster and Aftermath and another go, but I would miss the interesting character builds possible when everyone get their own subsystem.
I think tomorrow I will talk a little about Runebearer's "feat" implementation, talents and how that all came about.