art work, stained glass, statuary

Can you give more pictures of your style first? Colors you prefer?

I would drywall the whole thing.

Very simple decor on shelves, not too overloaded, love the hanging men from Etsy. What about a 3D wall panel or wallpaper in the above niches, could look effective or art

I think you should take the approach below: very simple, but with some variety in size and shape (the items on your shelves are far too small, and pushed too far to the back). I like the bit of repetition in this arrangement, too. There are a couple of shelves here with two items on them, which I don't much like. Think in terms of using one or three items per shelf, unless you have a distinct pair of objects that obviously belong together. Pairs tend to 'read' as one.

I particularly like, here, how the designer has formed a triangle using the three lower shelves in the middle, where the items get progressively narrower from the bottom.

Consider packing both your bottom shelves with books (in good condition, not the mucky old paperbacks, much as I love mucky old paperbacks). Alternatively, you could use two identical decorative shallow bowls -- a design that will look good viewed from above. It helps to have some visual weight at the base of an arrangement.

Some inspiration

well, first you need to get rid off the painting you have there ... it is not nice to look at not to mention way too small for the area. as for shelf space i put mostly books (as i have many) and family pictures in one of my homes, and some pictures and stained glass wear in the other home. as for the upper part? no idea. i probably would dry wall as personally i think so-called cathedral ceiling is such a passé, unless of course you want to make your living room look more like an alter in a cathedral.

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I'd also remove the glass shelf/wine rack(?) in the left-hand corner as it clutters the already busy wall.

Drywall. Why do builders put these things in! Total waste of space. The vents between the top of the shelves and the bottom of the niches is very distracting. So I would drywall the niches to create one solid wall. Art should be hung at "human" height, anyway, so ignore and wall space above 8 foot.

The fireplace is quite small for such a large wall. The tiny items on display accentuate the petite fireplace. And the big niches are too hard to decorate. The central art piece is very dark and is too small on that tall wall.
I would consider closing up the niches, removing one or two shelves in the two display cases and removing the extra display case completely. The built-in display cases could have a mixture of books on a few shelves and a few larger decorative pieces on other shelves. One taller piece of art (not wider than the fireplace opening) would be better balanced in the center, with smaller pieces to the side.

Two tall vases. I really like the suggestions for mirrors.

How about books ? Take the painting down ..it doesn't fit ..how about a tall painting or covering the two holes up with dry wall and hang a large painting over the entire fireplace ...? The fireplace is very small ...I would either rip the stone out or put black granite over it ...to look bigger ..!
You have to change the wall ...everything looks off starting with enlarging the look of the fireplace ......black always works ..just hang a sheet of black fabric for a couple of days from the mantle ..cut a hole for the fireplace and live with it for a few days ...you will see how much better the wall will look ...

great suggestions. we are thinking of a large mirror long as well in place of the black picture.

We like the idea of one large painting or one large mirror, but we wouldn't use the other niches above. Perhaps just drywall over it?

To me, bookcases need books. It looks great to include a few pieces of sculpture among the books, but those bookcases need books.