Just flew to and from Atlanta from LGW with Delta. I found the FA's to be friendly and curteous. One of them even cracked a joke about how Delta staff are looking for jobs elsewhere.
However, if the staff were fine, I found the experience as a whole less than positive. The IFE was poor (no seat back setup and the video rewound itself to the start when the captain made an announcement).
I was shocked to be asked to pay for booze. Even wine with a meal had to be paid for. I'm used to alcohol not being complementary on domestic flights in the US, but I've never seen this on trans-Atlantic ones.
Perhaps my biggest complaint however, was the seats. They were the sort of bus type seats that you get on short haul flights. No head rests or anything to make you comfy. It was a long nine hours on the way out.