Wasp:
Hexen III would be very cool. Granted, if you follow all the storylines though, it has been milked for all its worth. (Don't read on if you haven't played them and don't want a spoiler). You had the three serpent riders in Heretic, Hexen, and Hexen II, who have all been defeated in each game respectively. Then you have the mission pack of Hexen II dealing with some villian trying to usurp their soul-power. Finally, you've got Heretic II, which is a spinoff more than anything. It dealt with the hero of the first game and his curse from the first serpent rider he had slain.
At this point, all you could really have is a big pow-wow with all three resurrected Serpent Riders (kinda unoriginal..) That, or a remake. Heck though, Raven could pull it off I suppose, with the perty Doom 3 engine or such-- Raven has great artists and experience in the genre.
Love thy wookie.