Clerics have ten 4th-level spells in AD&D. Five of those have carried over from OD&D: cure serious wounds, neutralize poison, protection from evil 10' radius, speak with plants and sticks to snakes. Four are all-new: detect lie, divination, exorcise and tongues. The last spell - lower water - was in OD&D, but only as a 6th-level magic-user spell.
Cure Serious Wounds: A touch spell that heals 2d8+1 points of damage, which can also be reversed as cause serious wounds. The OD&D version of the spell is exactly the same, except that it healed 2d6+2 points of damage. Although the OD&D spell appears to be slightly less powerful, it should be noted that characters in that game had less hit points than those in AD&D.
Like cure light wounds, there are a number of creature types that this spell can't affect. This includes all creatures that can only be hit by silver, iron or magical weapons. I wonder what the rationale is here? From memory, most of the relevant monsters at this point are things like demons, undead, gargoyles, and similarly fantastical beings. Those kinds of creatures being unaffected by cure spells seems fair enough, but I feel as though there'll be monsters added to the game later that don't quite fit this mold. I'm tempted to tie this immunity back to Gygax's idea about creatures with immunity to normal weapons existing in multiple planes of reality. So far, it's the only concrete thing we have to go on regarding the topic, so I'm going to run with it.
Detect Lie: A new spell that allows the caster to tell if the target is telling the truth. It can be reversed as undetectable lie, which either counters detect lie or makes complete untruths seem reasonable. Detect lie requires gold dust to cast, while its reverse requires brass dust; in neither case is the value of the required dust indicated.
Divination: This new spell reveals information about an area such as a small forest or a section of a dungeon level: strength of monsters, value of treasure, and the chance that invaders will incur the wrath of a powerful supernatural being. The chance of obtaining accurate information starts at 60% and climbs by 1% per caster level.
The spell components required are incense, a holy symbol, and a sacrificial creature. Perhaps it's my background as a player of BECMI and 2nd edition AD&D, but I'm surprised that's in there. I wonder how sacrificing animals affects PCs of good alignment? I'd be inclined to be allow it. Lawful good clerics aren't forced to be vegans, so I don't see why they can't sacrifice a goat or a sheep or whatever. No humans allowed, of course. Hobbits are a toss-up.
Exorcise: Frees a single target from any form of possession by an outside force. It can also be used on any item that contains a creature's soul, and will force said soul into its nearest material body.
The spell description is written in the standard over-complicated Gygaxian style, so I'm not entirely sure how it works. I think the caster rolls d100 to randomly determine the base chance of success. That base chance is modified up or down by comparing the caster's level to that of the possessing entity or magic. The caster gets to roll every turn to determine success, and can seemingly keep rolling forever. To me it looks as though the spell will always work eventually, unless its interrupted for some reason. The chance of success can also be increased by using a holy relic, but that seems a bit pointless unless you need the spell to succeed really quickly.
Lower Water: What was one a 6th-level spell for magic-users is now available as a 4th-level cleric spell. It causes water (or "similar fluid", whatever that means) to lower by 5% per caster level. Area of effect is also increased by caster level, and the spell can be reversed to return liquid to its normal height. Material component is a pinch of dust.
The OD&D version of this spell lowered water to a flat 50%, so it's not as effective in that regard. It's range was 24" though, which is double that of the AD&D version. The duration was 10 turns, whereas AD&D has a duration of 1 turn per level. The OD&D spell wasn't reversible.
(I wonder, would blood be considered a "similar liquid"? Could you lower the blood inside a creature, perhaps causing it to pass out? The answer, of course, is "fuck off with that bullshit", but it's something to think about.)
Neutralize Poison: This spell completely removes poison from any creature or object touched. Not only can this be used to heal a character who has been poisoned, but it can also make a poisonous snake harmless, or remove the venom from a trap or weapon. Using the spell to remove poison from monsters is a genius move, and one I have never seen or thought of. I've read this spell description before, but only on a careful reading now am I realising that this can be done, and it's super-cool.
The spell can also be reversed as poison, which requires a touch attack and will kill the target on a failed save. Is this the lowest-level save-or-die effect? I think it might be.
The OD&D version of this spell was a bit vague. It was said to counter the harmful effects of poison, but specifically notes that it won't help characters that have been killed by poison. I guess the same applies to the AD&D spell as well: while it will purge the poison from the body, it won't restore the victim to life. Makes sense, I guess, but it does limit the spell's usefulness by quite a bit.
Protection From Evil, 10' Radius: Works exactly like protection from evil, except that the area of effect is a 10' radius globe around the caster, and the duration is increased. This means that it completely hedges out conjured or enchanted creatures (devils, demons, imps, etc.), inflicts a -2 penalty to attack rolls on all evil creatures, and grants allies +2 to saves. It can, of course, be reversed to affect good creatures.
The main difference from the OD&D spell is that that version only gave a penalty/bonus of -1/+1. It also had a flat duration of 12 turns, whereas AD&D gives a duration of 1 turn/level.
Speak With Plants: The caster of the spell can converse with plant life within a 6" circle. The spell is a little contradictory. It says that the caster can command thickets to part to enable easy passage, or make vines entangle pursuers. Then it says that the spell can't animate non-ambulatory vegetation. Which is it? I would rule that small movements like those mentioned above are possible, but that plants can't move from where they are rooted, or be commanded to make attacks with branches, or really do anything beyond make nuisances of themselves.
The OD&D spell is much the same as this version. The only significant difference is that the duration was a flat 6 turns, while AD&D has a duration of 1 round/level. (This could either be about the same or a significant drop, depending on how you interpret the use of turns in OD&D.)
Sticks to Snakes: Transforms one stick per caster level into a snake that can be commanded to attack. Each snake has a 5% chance per caster level of being venomous (though no indication of the strength of the venom is given). The spell can work on objects like spears and torches, but won't affect magic items. The spell can be reversed as snakes to sticks, either to temporarily transform regular snakes into harmless sticks, or to counter the regular version of this spell.
In OD&D the caster created 2-16 snakes, with a flat 50% that they were poisonous. The duration was 6 turns (as opposed to 2 rounds/level) and the range was 12" (which is now radically shortened to 3"). Overall, I'd say the AD&D spell is on average deadlier; as I read the OD&D version you roll once to determine if all your snakes are poisonous, whereas in AD&D you roll individually. Individual rolls mean that you're bound to get some poisonous snakes, and the chance goes up as you gain levels.
Tongues: A new spell that allows the caster to speak the language of any creatures with 6". It even works on alignment languages, which is slightly surprising. The reversed form of the spell makes verbal communication within the area of effect impossible. I can see players attempting to use this version of the spell to disrupt spellcasting, but I would absolutely not allow that. Spells are a means of manipulating reality, and not a form of communication.