I'm not talking about the image of the holier-than-thou, plate mail wearin', forced converting, mace-slammin' cleric. I love that guy. Look at that guy. You see that moustache? He's about to cleric the hell out of some orc tribesman, and not even feel bad about. All in the name of Pelor, my friend.
What really bothers me is, well, three things, I guess. They make me have to define and regulate religions in my game, to the point where without a complete cosmology and set of rules and strictures for each deity that I'm not using all the design space. Clerics use divine magic, which is exactly the same as arcane magic except the spells are different and they know all of them, and clerics, well, are weird.
Lemme start with the last one. Clerics are crusaders. They are paladins without the name (and one the reasons I never saw the need for the Paladin class, to be totally honest.) They're holy warriors with the literal powers of the gods. Their spells are all healy, they believe in one god above all others- they're bizarre monotheistic warrior-priests in a world with ten thousand gods. At least by default there's ten thousand gods. I quibble.
The point is, now I have to sit down and write at least a couple of blurbs about each god. They've got to have names, and stuff they cover, and relationships, and rules, and regulations, and I hate it. I don't like coming up with names, and I don't like designing an entire pantheon from scratch to have a cleric pick one guy and go "ok, that's my guy, now he's giving me powers, right?" Now, look. I'm not a religious guy. I've never had any sort of god talk in my ear, or give me magical healing powers. But it seems like this is taking all the mystery away from the world. There's no "we interpret the will of Zeus through oracles and the entrails of sheep." It's all "Shit, just talk to the guy! He's right there. We got a scroll of Commune right here, bro!" Not satisfying to me in the least.
I mean, seriously. There goes the entire world's moral dilemmas. You can't say that what you were doing was right when the representative of the god of good stuff phoned him up and says to you, "Actually, that wasn't morally justified in the grand scheme of things- see, you actually caused more evil for future generations by dealing harshly in this instance, etc etc etc." Awfulness.
The real reason I dislike the, though, is that clerics feel like wizards. They have Vancian magic from the gods. Just something about that rubs me the wrong way. I don't like it. In my mind, clerics should have their own thing going for them. They shouldn't be a fountain of heals, and they shouldn't be a walking pile of useless. Part of the big problem is giving clerics an identity. There are plenty of minor horror stories about people playing clerics and then being expected to use all of their casting slots on heals, to the extent that their character's entire role in the game is running around and healing people until they're out of spells. It's not a whole lot of fun playing a role because somebody has to do it or we're all going to die. But it's also not a whole lot of fun to play a class that doesn't bring anything to the party.
Between Fighters, Thieves and Wizards, you have the big strong guy, the sneaky subtle guy, and the guy with a lot of magic. What else is there, really? You've named the Holy Trinity of character roles. It's big enough that there's at least one system that defines your characters entirely by that, and you can still have cleric surrogates in it.
I think Monte Cook puts it about the same way I do, except maybe better:
(...) I tried to step back and say, "What kind of characters do people want to play?" Well, there's the skillful guy, there's the guy who uses magic rather than physical force, and there's the big tough guy with a sword. D&D addresses these roles by providing the rogue, the wizard, and the fighter.
As an aside, although I know there are plenty of people who like to play clerics, I've seen that many players consider playing a cleric a "necessary evil," rather than their first choice. I think this is because, while D&D pretty much requires a cleric's presence, it's not one of the basic roles people like to play. (Cleric lovers, please don't send me angry emails! I like clerics! But we all know that cleric lovers are a minority.)
I think that, if anything, wizards are going to wield god-given magic, and maybe stick the healing spells in with the arcane spells. I've seen it done before, and it seems a whole lot cooler than having "utility wizard" and "healing wizard with armor and maces". At least in my mind. There's nothing wrong with Clerics, they're just not really design space I'm interested in.