Up to now, I've avoided the 787 because I principally fly UA in economy and, reportedly, UA's 787s in economy are awful.

But I've just done a perfect test. AC in Business. One way I flew the 787-9 and on the return their newly fitted 777. So they were identical products with identical seats. There was precious little difference. The windows on the 787 were larger and, despite myself, I didn't mind the electronic, rather than physical, shading and in fact quite liked it, although I didn't like the fact that the FAs had an override.

Otherwise there was no difference that I could tell.