More pictures:

Bumping to see if anyone has ideas.

I would use two panels of gauzy or sheer curtains on a pocket rod so they stay in place. I would let the left one hang straight and the right one be pulled back with a drapery piece shaped like a fish hook. That way you will have a visual with as much light showing on the right as the left. Or you could use the pocket rod on the insider of the window so the molding is showing and use just bottom ones or full length, again I'd get gauze or sheer..

You have such great pieces in the nook already, I wouldn't add a heavily patterned curtain. I would probably do a textured linen panel.

Are you more worried about the extra wall space on the right or covering up the window on the left with the smaller return? Or both?

I would probably just hang panels evenly around the windows and ignore the extra wall space. But I don't have to look at it every day.

Have you thought of trying a Roman Shade?

Select Roman Shades · More Info

We've got a few pleat styles to choose from to add a little accent to the window too.

https://www.selectblinds.com/romanshades/reserve-solid-roman-shades.html

I would just hang straight panels in a light breezy or linen look. If the exposed wider section of wall bothers you, hang two small pictures for balance.

Thanks so much for the suggestions! I like the idea of sheers or lightweight linen and I think I'll try them (actually, I had sheers in a couple of places I lived years ago and loved them).

d_gw - I'm not so concerned about the space on the left but I couldn't quite wrap my head around the limited space on the left side. I kept thinking about a panel on each side and that there just wasn't enough room on the left side for panels to look right.

Very nice room! I like the idea of sheer curtains or lightweight linen. Elegant and simple.

There isn't enough room on the left IMO, unless you don't mind covering a lot of the window. Because of the large width, they'll look skimpy if you stack them all the way over.