Unfortunately, half-decent is as good as it gets at EWR. I would expect that at that hour of the morning things would be open. However, I'd keep your expectations low - I assume you'll be able to get a hot breakfast with the usual eggs, bacon/sausage, toast, potatoes options. But it's likely to be mediocre.

A quick google search pulls up some place called Eggy Weggy, which has some pictures to give you an idea of what's in store:

https://www.yelp.com/biz/eggy-weggy-newark

In short, EWR is a garbage airport and food options aren't great.