* Character ability scores start really weak, but grow MUCH faster than normal. You start with 63 ability score points that you may allot in any way you like, non-weighted. That means no point buy rules where higher scores cost more -- one point costs one point, whether it's an 11 or an 18. You may allot your points 10-10-10-11-11-11 or 3-3-3-18-18-18. Basically, you start with as many points as an utterly regular jane.
However, to compensate, your ability score points increase by 2 every level. So at level 4, you will have 69 ability score points. At level 8, 77 points. At level 20, 101 points (which maps out to the equivalent of a 16-17-17-17-17-17 array). Although that is just for purposes of illustration; the games I run will probably end before level 20.
There is a cap, though, and it's the same as in base Pathfinder: no ability may be higher than 18 (before racial modifiers) at levels 1-3; no ability may be higher than 19 (before racial modifiers) at levels 4-7; no ability may be higher than 20 (before racial modifiers) at levels 8-11; and so on.
* Hit dice are according to D&D 3.0/3.5. That means wizards/sorcerers have a d4 hit die and rogues have a d6 hit die. Classes that have only existed in Pathfinder will follow these guidelines and will be matched to the closest D&D class. For example, the witch, as a 9-level arcane caster with 1/2 BAB will match the wizard and sorcerer in having a d4 hit die. A lot of Pathfinder classes will probably take a hit in HD size, so brace for the worst in that regard.
* No male main PCs. Main PCs may be female, intersex or m2f trans. This is due to what I feel is an overrepresentation of male heroes in fantasy. I want to see ladies save the day. Secondary characters (such as Leadership cohorts, spiritualist phantoms et al) may be of any gender, including fully male. Players may of course be of any gender, there is absolutely no restriction on players whatsoever.
* No core races except humans. No elves, dwarves, halflings, gnomes, half-elves or half-orcs. Sorry but no. I will literally start cutting myself if I ever have to play with the races I've been inundated with for the past 30 years of this hobby. I'm done with them. Done. I'd much rather you give me something weird like a fricking vanara or tengu (although I do admit a preference for humanoid-headed characters over animal-headed, but it's not a 100% rule). Some of my favorites are aasimar, tiefling, sylph, changeling, samsaran, android and lashunta (not in that order).