I flew DL from BRU to JFK in C+ about 10 days ago and we received:
- nuts and drinks;
- lunch, which was decent, but not up to AF standards;
- ice cream;
- and a box with a disgusting sandwich and a tiny dessert.

Not including the apéritif or digestif this was very similar to what you would get on AF or KL. We didn't drink wine so I can't comment on the quality.
It's been a while since I flew direct to ATL on DL, but I cannot recall a third meal. KL served two meals the last time I flew this route, with the second one being of far better quality than the throwaway sandwich DL offered to JFK.

I agree with NLNO that the DL crew frequently did water rounds, but I do believe this is partially dependent on the crew's own initiative. Generally speaking I would agree with Goldorak and say that AF is my airline of choice in Y between AF, KL, and DL. I've never felt that the AF crew was too absent and they've always answered with a smile when asking for anything. We flew back from ATL on KL a few days ago and while the food was mediocre (ex-US is always worse than ex-Europe) the crew was excellent and generous with drinks.

Overall, I feel all three offer a similar product, with AF winning the food trophy and KL winning the crew trophy. Entertainment was more to our liking on KL than on DL. That said, we very much enjoyed our last flight on DL and would still be happy to fly them in Y over many competitors. It certainly doesn't hurt that DL offers better perks to FB Silver than AF or KL do.