This brief thumbnail sketch, I think, demonstrates what I'm trying to achieve in this campaign and how I'm getting there. I'm trying to give the game as much of an "old school charm" as I can, and I'd say it's working. We have the greater-evil-behind-the-bad-guys theme that the early Greyhawk modules used so well (hill/frost/fire giants in turn controlled by drow), as well as the non-monolithic nature of evil (the drow riven by internal rivalries and beset by their own external foes in the underoerth such as the illithids). We have the "old reliable dungeon crawl" close to hand in case the PCs get restless and decide to simply go kill things and take their stuff (in their case, they very properly saw the potential to gain treasure and experience in the dungeon to improve their chances of taking on the bandits and the witch). We have the gee-whiz factor of completely new and unknown magic and powers; my witch isn't to be found in any rule book or magazine article. There were also a number of very memorable NPCs (I tend to do different voices for my NPCs, so that's a lot of fun for me). Plus, I tried to introduce more than a little humor in places (the succubus secretary, a faerie dragon named Flibber who ended up joining the party as an NPC, etc.) and was not too uptight about introducing the occasional anachronism (the devilish attorney, for example, used an intercom and had a modern office tucked away in an interdimensional space). I was very consciously not trying to maintain a "pure" setting so much as a "fun" one, and I think my players (none of whom had played AD&D before) are really liking the approach.
Also be sure to check out the witch spell ylfe-shot.