Day-to-Day Acquisition of Cleric Spells: There's some neat stuff in here that I'd completely forgotten since my first edition days. I love that Clerics cast first and second level spells based on their own divine power; if a deity withdraws his or her favor from a cleric, she does not lose her first and second level spells as a result. Even a change in alignment will not cost access to such spells, so long as the change is embraced with as much fervor and zeal as the original path the cleric trod.
Third through fifth level spells are granted in turn, not by the deity itself, but by powerful servitors of the god or goddess--angels, demons, yochlol, devils, archons, and other supernatural minions impart these abilities as mediators between the cleric and deity. This is of great interest, since now the cleric needs not only follow the strict tenets of the deity, but has to avoid pissing off or foiling the personal ambitions of its all-too-free-willed minion as well. Nobody ever said being a cleric should be easy.
This also opens up really interesting options for play; what if a cleric violates the tenets of his god, but the deity's angelic minion has fallen madly in love with the cleric? That minion could, feasibly, still grant powers. Where such a storyline would go is not in the purview of this thread, but it opens up intriguing possibility for drama and epic play.
It's only when a cleric gains access to sixth and seventh level spells (remember in first edition cleric spells only went up to level 7) that a direct line to the deity is gained. At this point the cleric has gained high enough level that the gods themselves sit up and take notice. There is also an unwritten implication and assumption that in AD&D, gods are not truly omnipotent. A deity doesn't provide spells and powers to low-level followers simply because he cannot be everywhere at one time. This also provides a convenient answer to why the gods don't solve all the world's problems.
This is stuff that most folks glossed over and just plain missed back in the day, but adds some interesting tweaks to the game. Unfortunately, TSR never really followed up on it, either. We never saw, for instance, the ranks of holy servants who dealt with clerics for the different pantheons listed in the Deities & Demi-gods book.
I'm considering resurrecting this sort of thing for my Moldvay/Cook/LL hack. Heck, I'm considering crafting a separate class of cleric for each deity in my game. That, however, looks like too much work. Hopefully, I'll be able to work something out that doesn't require so much effort.