Buy some glass paint!  Choose your design, maybe enlarge it or project it onto the glass, paint it on like a leaded pane (like you'd find in a church).

Bright, airy and easily removed or updated!  If you feel you need to block out the light or to cover the expanse I'd go for a portable screen. Non permanent and decorative.  It could be used elsewhere in the house.  The frame is easily made and the fabric to your choice easily applied.  If I had a scanner I'd send you a "how to".... Am on it!!!

http://wallpaperforwindows.com/

I have french doors with unpaned windows in the master bathroom. I've been thinking about this site on top of some others. This one seems to have the larger sized films I would need for unpaned glass (large enough to cut down instead of trying to purchase extra and line it up).

I haven't used the product yet but thought it may offer you more options. Let us know what you do. 

I'll "me too" what someone else suggested, for the windowfilm -- if you want something a little "bolder", Home Depot and its ilk also sell the same films designed to look like stained glass (although on a window that size, the repeating nature of the pattern might make it too cheesy.)

If you don't mind altering the glass altogether, consider doing a stencilled glass etching.  It's permanent, but you can cover as much or as little of the glass as you want, use a design (like ivy or leaves) or something abstract (like blocks)

 When I read your post, I immediately thought of these transclucent window coverings featured in this design*sponge feature.  http://www.designspongeonline.com/2007/10/window-films.html

It lets the light in while covering what is behind it.  Covering your sliding doors make me think they could be turned into Shoji screens.

 Good luck!