Sweet side scrolling goodness baby! There just aren't enough cool side scrollers being released. Though I am very partial to a more puzzle/maze oriented scroller when done completely in 2D (think Prince of Persia, Zorro, Blackthorne, or Nosferatu). In fact, I'd love to do a sequel, remake, or game in the style of Nosferatu, which was one of the most anticipated SNES games but flopped due to poor game controls and horrid enemy AI.

P.S. My second choice would be a RTS.