Ye olde cleric suffers from but one underlying problem. It is a class that screams out for religious specificity but it is generic as hell. Are we seriously to believe that priests of Kindheart the Good have the exact same restrictions and spell lists as priests of Cutheart the Wicked? I don't think so.
And sure, the text of some versions of the game will tell you to use your common sense and limit spells that might appear to be evil to those clerics of evil deities. And that's fine and dandy. But what about this ban on edged weapons? Clerics of Slitty the God of Knives can't use knives?
Like the thief, the cleric has has its fair share of debate and house rules over the years. And this is another example, in my opinion, where the Second Edition of the game really seemed to address the problem and kinda got it right. If you haven't read the 2e description of the Priest in a while you should check it out. The whole thing about spheres of influence is a bit fiddly for me and kinda restrains things but it's a valiant effort to make priests more interesting to play (for the record, the “cleric” is the generic priest class of 2e... the good old class we all know and love).
I'm not breaking new ground here. But this is how I handle clerics and how I'll be handling them moving forward. The stuff I'm rattling on about below is not always clearly defined. This is because each campaign may have a totally different set of gods or a different way of interacting with divinity, if at all. If the thief is a specialist who is self-determined, the cleric is a specialist who is utterly constrained in their choices once they make the choice to follow a path of worship and service to a higher power. Those constraints should be tailored to suit the campaign if you want the reveal a fuller range of the cleric's great potential as a character class.
Anyhow... this is what I do...
PRAYER ROLL: Clerics have to pray for spells. I allow them to choose any spell from their list without preparing them ahead of time. Instead, they pray in the heat of the moment for miracles! This is a huge benefit. It turns your spell list into a Swiss Army knife, though you still have the same number of spell slots.
The catch is you have to pray for the power in order to cast it. So the player rolls a d6 and on a result of 1 the gods are deaf, ambivalent, or downright snobbish and refuse to grant the power. The spell does not work.
I fooled around with fiddly rules that would account for falling out of favor, changing the die type up or down. But in the end I think that sort of thing works best if left entirely up to DM fiat. If the cleric is acting obviously out of alignment with their god, then the DM could change the failure range to 1-2 on a d6 until the cleric atones and corrects their behavior.
In the first campaign I ran using this rule I had a situation or two in which the cleric was in very good favor and I either waived the prayer roll for one or two spells or I had the player roll a d8 instead. But those rules are not codified and I don't think they should be.
SPECIFICITY: If I'm running a one-shot at a con or something like that I'll just use the cleric as-written (with the prayer roll). But when I'm doing a campaign or I have more time for prep I want deity-specific clerics. What makes the priestess of Jeff the God of Chairs functionally different from the priest of Bonan the God of Beheading? If there's no functional difference then the religions become all color... kind of meaningless in game terms.
So I'll usually do one or two or all of the things below in order to define a cleric of god X vs. a cleric of god Y.
- Change the turn undead power to something else. Maybe it doesn't make as much sense for a priest of the god of machines to turn undead. Instead, maybe they control golems and automatons using the same rules. In my home campaign, the clerics of Frimm the War God can summon the spirits of slain warriors to fight with them instead of turning undead.
- Change the banned weapons. It makes sense to limit weapons and armor if it seems like the god in question would care about those things. So play with that idea. I have one cleric sub-class who worship an evil deity that only allows them to tote specially cursed ritual daggers. Another sub-class worshiping a god of tricks and thievery may only pack small weapons that are easily hidden.
- Limit the spell list. This one seems simple but can lead to more work than you expect. Depending on how vast your cleric spell list is, you might find it hard to come up with appropriate spells in the right numbers. You might have to... invent new spells! I heartily encourage you to do so. After all, doesn't it make sense that Jibber the God of Babbling has a handful of spells related to talking? And why would a priestess of Rikki the God of Mongooses have any interest in turning sticks into snakes?
- Set requirements for the cleric that aren't related to spells or combat. A cleric is not a priest of the temple required to be in attendance day in and day out but they ARE a representative of the god abroad. So they MUST show people what their god is all about. That might require proselytizing, preaching, and cajoling for new converts. Or they might belong to a secret order and might actually hide the fact that they are a cleric at all. They might merely be required to spend x turns per day making a sacrifice or reading a sacred text. If you feel like you've given the cleric a few too many bennies in other areas you can hit them hard with daily requirements and restrictions on behavior. See the classic paladin class or maybe even the cavalier for examples of that. Of course it CAN get silly if you go too far... a cleric of Jeff the God of Chairs should not be required to sit in every chair they find... right? Hmmm....
I guess the trick is to play an intuitive balancing game with the cleric if you're going to make each one god-specific. Personally, I TRY to keep the standard cleric XP table intact no matter what I do. So all clerics advance at the same rate and have the same number of spells. Then I just try to make sure each one's special strengths are balanced against the others. You don't have to do it that way, but that's what I choose.
And ain't that the great thing about screwing around with this game?