I have flown ARN-ADD-CPT return in business class 1½ year ago. Nothing posh or spectacular but still good experience. The meals served (Etiopien food was also available) were tasty. I found the seats on the ET B772 to be better than on the newer B788 (despite the 2-3-2 configuration as opposed to 2-2-2 on B788)

I wouldn't hesitate to book.