Have you tried using the terrain engine for your landscape? That will probably look better and be easier to make.
I’ve worked on a couple first person shooters with Unity, one was Megapixel which was a solo effort for a contest and the other is avert fate which I only did the programming and effects on (this guy did all the modeling and textures, and he had the original idea)
Our team at Wanilla is making an FPS called Colorful Planet. Of course, true to Wanilla style it won’t be very realistic or dark, so I’m not sure how much it will help you.
We’re doing it strictly online multiplayer for now (though some day I’d like to flesh out a single player mode for it). I’ll post some screens later so you can get a better idea of a whimsical FPS