Shade Gardening: Help, I keep drawing a blank on my backyard., 1 by Magwar

Magwar wrote:
As you all know I have been doing some major remodeling of our house. I am completely stuck on what to do with the backyard. Most of it is on a slope. We think that it used to be a field because terraces are cut into the soil (ridges). My husband wants to plant grass but I think it would be a pain in the neck to mow, but we also have to think about us having kids (they need a play area) I have been told I can't add more soil due to the trees back there, and we have a bad wash from the nieghbors yard. The majority is shaded so really kinda stuck on what to do.

Any ideas? Pictures that might give me some sort of push? I am royally stuck. The red lines are our property line. The only flat spot is the spot I was taking pictures on. (we want to move the trampoline down there but again, there is no walkway or nothing...)

Also the way our property is situated, I don't want to go in any lines across the property like the previous owners, to me it makes the odd shaped property stand out more (the oddness of the shape)