Wow looks like an amazing space switch so many opportunities. Before you touch the wood, try hanging large format photos or giant paintings. Instead of loading the built ins with books, try large light colored pottery. Flooring I hope will be wood (it would be a shame to use vinyl!!!) and then a light color rug. Lots of good lighting. Plants. Your desk can be white or marble topped for further bright. White drapes to surround the windows. That will offset the wood walls and ceiling.

This is all new, not precious wood, most is plywood. If you love it, awesome. Otherwise I would hire a trim carpenter to simplify the mantle and bookshelves (remove the arches, flutes, and keystones) and paint it all white. The room would still have wonderful detail but be much more refreshed.

Experiment a bit first. Cut luan or foam core to fit the backs of all the deep recesses. You can paint or paper them to add some life to the monotony. LED lighting inside the cabinetry could help tremendously, as could art on the large expanses of wall with art lights above them.

Home Office - Needham Custom Home - 02 · More Info

you could paint INSIDE the unit(s) to brighten things up. also between the ceiling beams.

I would remove it all. No office needs that much storage in this modern world. Sheet rock the wall, paint the ceiling between the beams white.