I've thought up the concept for my 4e4 game already. The game will feature a metal gearish style of gameplay, favoring stealth over run and gun tactics. And yes, it will feature ninjas, pirates, robots, and zombies.

Of course, the game will require some pretty advanced AI code, which I'm going to enjoy immensaly. AI has always been my favorite part of game programming, even though I have never made a game that required AI.

The game will feature intelligent ninja, robot, etc, guards that can act semi-intelligently. The goal is to have enemies that can call for backup when they see the player, and attack in formation. I've already mapped out in my mind how the AI will work. Basically, it will use a Finite State Machine to control the actions of the guards. I'll post some example code tomorrow, once I fully flesh out how this will work.

Oh, and this game will be open-source, so maybe some people will be interested in what I did with the AI.