Books, you need books.

Books belong on bookshelves!

They look great now, except for that shady top part, which is weird. Having a blank white space contrasting with it above the tv makes it look even more weird. I'd hire a cabinet maker to lop the top off of the bookshelves, extend the supports to the top of the wall, and put the crown molding in the alcove, at the top of the wall, not leave a dark space there. Then I would put some kind of decorative wall curlicue above the tv. Heck that's even a spot for some judicious stenciling or even the dreaded word art. But I would address the shelving issue first.

Or if you really don't want to fix the shelves, then just some type of flat wall curlicue to fill in the blank space above the TV, in white to match the shelves. Then call it a day. Less is more.

I tried to find and example but couldn't easily. I'll bet you could find something in an antique or salvage place that you could paint white.