What about a game like "Commandos: Behind Enemy Lines" ?

- Top Down View
- Make Enemy's "line of sight" visible (via model or bitmap)
- Setting could be anywhere on the world (maybe during a war between two fictional lands)
- Gameplay focuses on avoiding the enemy, planning safety routes, distracting the enemy with an object (like a stone or cigarrette pack or bottle) and killing him from behind (with a knife etc...)
- Thus there's no gunplay, no grenades or other fancy effects
- If the player comes into the "line of sight", the enemy will directly run towards the player/shoot at him until the player exits the "line of sight". If this happens, a marker will be placed and the enemy will try to reach that marker. If he reaches it, he'll stop and look around (~ 10 sec). If he can't spot the player while looking around, he'll go to his last position/patroul marker and start guarding/patrouling again.
- If the enemy sees an object (like bottle with beer etc...), he'll try to reach it. When he reaches the object, it will be delete and the enemy will play an animation (like drinking ~ 20 sec). After that he'll go to his last patroul marker and starts patrouling etc...
- Also it's a top-down-view, we can build buildings with multiple floors. All we have to do is to create some big, invisivle objects which check if the player collides with them. If for example the player collides with "Floor.2", then "Floor.1" and "Floor.2" will render all the meshes and entities which are also colliding with them, while "Floor.3" and "Floor.4" and "Floor.5" etc... are keept invisible

That's all I could come up with (for now ^^)
If you search for a level designer, I might try to build some maps since I'm mapping for the "Thief: The Dark Project" community for nearly 5 years now. I was also one of the "beta-mappers" which worked on the "The Dark Mod". So, if you need someone who might map you some levels for your project, let me know and I'll see what I can do.