Sorry, I thought I mentioned it. I'm using Pathfinder for the system, but with my own races and classes, and misc. other homebrew features to accommodate the unusual play style.
I've adapted several CR 10 Aberrations into a playable race template. They're still leagues more powerful than a human or orc, but you'll be starting at Level 1 just like always. The options are: Bee-Man, Brume, Chyzaedu, Crimson Death, Delver, Emkrah, Gug, and Yithian.
As for the classes, I have designed three:
The Farplanar - A modified Skald that borrows from Druid and Cavalier. The Farplanar will be magic-heavy, with powerful rage and challenge abilities, and the power to transform into animals, magical beasts, and even other aberrations.
The Hierophant - A modified Warpriest that borrows from Alchemist and Summoner. The Hierophant is something of a battle cleric, with magic potions and devastating bombs, and the ability to Spawn lesser horrors.
The Shade - A modified Monk that borrows from Rogue and Witch. The Shade focuses on the natural weapon attacks I have removed from each race, like awful bites and eldritch tentacles. By playing the Shade, you get full use of your natural (or should I say, unnatural) powers back. It will also focus on sneak attacks and all kinds of creepy magic.
But of course, these features are the least of your arsenal. As abominations from the great beyond, your task will be to corrupt the minds of mortals with your dark signs, forbidden lore, and other devious tricks, as well as starting and managing your own cult! Foster their ranks until you can break through into the world of man!