Just out of curiosity, where do you come down on things like:
1. Paladins or clerics having a code of conduct (or, for that matter, classes with required alignments like druid, monk, etc)?
2. Classes like monk, druid or assassin with a built in "challenge an npc to advance to high levels" restriction?
3. Classes like assassin, monk or druid with a built in maximum level?
EDIT: For clarity, I'm talking 1e style here.
To be clear, while I started buying and reading D&D in 1e; I didn't play or DM until 2e. So this is mostly what I think I would have done, not what I actually did (not having the opportunity to).
1. These are role-playing restrictions, not mechanical penalties or limits, and they are in effect from 1st level onward, so they don't bother me very much. Most campaigns (Greyhawk; Forgotten Realms; mine) seem to have enough gods that you can find one that suits your taste. There's not a real cost associated with the druid or monk's alignment restrictions. The paladin's code is subject to DM interpretation, but it mostly requires good role-playing.
2. Again, it's really a role-playing scenario. Except for the druid (who gets bonus spells), you could just ignore this. Also, there's a strong element of player choice at work. The player could set up the challenge to give herself an advantage (in the assassin's case, they are expected to!)
3a. I'd probably have ignored the assassin's max level. Personally, I think the setup is a real game-killer anyways - I mean, you get all this XP looting dungeons and slaying dragons, and suddenly you're the head of all the assassins everywhere and expected to run the international assassin's guild? Paperwork, man, paperwork. Drowning in it. No fun. Also, with the possible exception of druids, I don't believe an assassin in medieval Prague really has to discover and journey to Australia to advance to 15th level. It makes more sense to me for the restriction to be by guild or order.
3b. Unearthed Arcana solved the issue of druids and maximum levels to my satisfaction. Also serves as an illustration that there might be something beyond 15th and 17th level for the assassin and monk.
3c. I don't know about the monk. I never liked the monk anyways. Or halflings.
