For the Labyrinth Lord campaign I've been running I've presented the character classes as archetypes, the essential representation of a particular way of overcoming obstacles, achieving goals, etc. This begs the question of whether there are other archetypes--one that's not easy to answer. I see perfectly valid reasons for allowing the negotiation of lots of other classes, and for restricting characters to one of the basic ones.
I'll give an example. One of my players wanted to play a character along the lines of Han Solo, so we started him as a thief. We figured that Shawn Solo (yes, that's his name) was sort of a shady guy who outsmarted enemies more often than whacking them with something. That went well for a while, and the player (being a newbie to RPGs) did an excellent job of roleplaying Shawn Solo. In other words, rather than conforming his character to the stats and mechanics of the thief class, he played him the way he thought that character would act and behave. This is where the thief class became a bit cumbersome. We realized that Shawn Solo was no more likely to pick someone's pocket than the fighter, and that he would actually be conking somebody on the head almost as often, especially if that someone was a nasty creature. He just happened to want to use a combination of stealth, trickery, and combat.
So...I broke my own rule a bit and we made a Bounty Hunter class. I don't feel that it fits the "archetype" explanation of what a character class should be, but I realize also that there's no reason why that has to be the only explanation. The Bounty Hunter we created is basically the thief class (saving throws, hit dice and 4/7 of the skills; no heavy armor, etc.), except he uses the fighter attack matrix. This seemed to fit with my player's understanding of his character, and was a fair trade-off, in my mind.
Now another dilemma has struck, though. I just read and loved Trey's description of the exterminators on his excellent blog--loved it so much I cut and pasted that bad-boy and read it to one of my players (he works on the other side of the wall from me). We both loved it and thought about how that would work as a PC. The character would need some special skills, but could really be of any class. The dilemma may not be completely apparent here, so let me explain. I HATE SKILL SYSTEMS. I've played a bunch of games with 'em, from Call of Cthulhu to TMNT, but I still hate 'em. I hate picking them during char gen; I hate watching players scour their character sheet for a skill instead of just describing how they're going to pull off an action, and I certainly hate updating skills as you level up. I know this animosity is disproportionate, but hey, I never said I was normal. So the fact that I'm getting close to coming up with another skill bundle makes me very unhappy.
Anyone got an idea for me? How do you modify character classes, or create new ones? Do you even mess with them at all? I'd love to hear more on this.