My ODD D&D will feature a few other changes. I've tinkered a bit with the races, and come up with what I think is a good mix (see last post with the tag) and I've ruled that "magic" doesn't exist, only psionics.
Of course, this is a bit of a facile statement. Psionics, as described in D&D, is magic, pure and simple. It even mimics most of the same effects as "magic" but it does so with an only marginally different rules system. Saying that there's no magic, only psionics, is somewhat disingenuous given the fact that psionics is magic, pure and simple, and the differences between a psion and a wizard are only slightly cosmetic. That said, it'll make the game feel less like D&D and more like some other fantasy heartbreaker, and that's the point--playing D&D but not making it feel like D&D. As a "hook" for a campaign setting, that's kind vague, and swapping out a bunch of classes is significant, but ultimately, what does that actually mean for players that this is using D&D rules but shouldn't feel like D&D?
I think what ultimately needs to be done is to ensure that the "story" of D&D isn't repeated. By this, I mean--what do D&D characters do and what are they about and how can I make sure that I do something different as a unique hook for this setting? To simplify greatly, the entire premise of D&D is that you create these characters that may be vaguely reminiscent of characters from The Lord of the Rings, but then you do a bunch of stuff that is nowhere reflected in any fantasy fiction other than a few purposefully derivative books that are trying to feel like a D&D session. To quote JB in one of my favorite rants of his, "Going into dungeons (“adventures”) and fighting monsters/picking up loot, all the while growing into more powerful characters, gaining neat “special powers.”" is the point of D&D, and as he also says, that's incredibly dumb. Well, whether or not you think it's dumb, clearly that's the premise and story that we want to avoid. If that's what D&D is, then this game, even while using strictly D&D rules, cannot be about that. Rather, it has to be about something else entirely.
I see this as a vs. campaign, with lots of political maneuvering and exploration of hostile wilderness. The world of ODD D&D, whatever it ends up being called, is one in which the PC races--the mammals--are the minority. Lizardmen (or lizardfolk as the more politically correct Wizards of the Coast have now renamed them--a bit sad that Games Workshop has totally kept up their backbone and not gone PC on us, while Wizards of the Coast led the PC charge) are the main antagonists, and along with their bigger blackscale cousins and a bevy of domesticated big lizards and dinosaurian animals, have over run a large island (about Greenland sized) of hostile wilderness. The humans (and other races, included half-orcs, goblinoids, etc.) live in isolated enclaves high in the mountains, or in other places that are more remote or inaccessible, and cross through the mainland like sneaking spies, hoping to not be stopped, killed, enslaved or eaten by the saurian overlords of the island.
Desperate runs through "lizzie-space" followed by intrigue and skullduggery in their fringe towns and cities, followed by (perhaps) open warfare with wave after wave of attacking lizards at times--that's what ODD D&D will be about. There aren't any dungeons.
Oh, and I'll be borrowing a ton of stuff from Games Workshop I think, in terms of lizardmen social structure. Freaky bloated mage-priests rule, and lots of domesticated and somewhat unrealistically ferocious dinosaurs are fixtures of their society. Have you seen their stegadon models? (Stegadon is not a real dinosaur, by the way.) It's got a Triceratops like frill and body (roughly) with a spiked mace-like tail and big, sharp teeth. It's like a "greatest hits" of dinosaur features all rolled up into a monstriously unrealistically ferocious package. And that's only one of several large monsters that work with the lizzies. I think the way to do this is to start with dinosaurs from the Monster Manuals and give them a few extra attacks of various types. Bigger, worse bite attacks, mace-like tail bludgeoning, poisonous breath-weapons, rake attacks--all in all, simply make the dinosaurs even more savage and dangerous than they already are, and I'll be good to go with monsters for the setting.
Add to that even more dark magic and weird one-off threats here and there, and I've got a lot to keep me busy. But the vs. Lizardmen theme is one that should be dominant.