The DUB-ATL with Delta is flown on their 767-300, which currently only have overhead tv entertainment in economy. Economy Comfort is the first 4-5 rows in economy, which, like other posters have commented, is essentially the same service and seats as 'standard' economy, but just have 4 inches more leg room and a little more recline. In my opinion they're not worth the extra money, but each to their own.
As for Delta. I've flown them many times, including these 767-300s. I had no problem, and had a book and iPad to keep me entertained.
I have read that Delta are in the process of upgrading their entire fleet to have AVOD in each seat in economy. I don't know the exact timescales, but it is possible they might have done it for your flight by the time you fly.