I've got two normal suggestions and one strange one:
1. Another Planescape game; not a sequel but once again pitting the player against the weird multiverse, and a return to Sigil, of course.
2. A cyberpunk game based on Neuromancer or Stand on Zanzibar/The Shockwave Rider. There are so few cyberpunk CRPGs it's a crying shame considering the richness of the literature.
3. Explore the zaniest tabletop RPG ever created: RIFTS! Frankly it'd be a challenge but an awesome one at that. This is a setting that has everything and the kitchen sink thrown in: Mecha, Dragons, Wizards, Aliens, Demons, Vampires, Plasma Cannons, Powered Armor, Zombies, AIs, Elves, Demigods, you name it, RIFTS has it. It's stupidly brilliant and I'm sure Obsidian could polish it into a black diamond.
http://www.palladium...s/what-is-rifts
Oh, and they have to be:
1. Turn-based combat.
2. Party gameplay
3. Story and dialogue-driven.
Thanks!